Historians have postulated that, without Bletchley Park, the Allies may never have won the war.

But, despite an impressive contribution to the war effort, the Bletchley Park site, now a museum, faces a bleak future unless it can secure funding to keep its doors open and its numerous exhibits from rotting away.

The Bletchley Park Trust receives no external funding. It has been deemed ineligible for funding by the National Lottery, and turned down by the Bill & Melinda Gates Foundation because the Microsoft founder will only fund internet-based technology projects.

"We are just about surviving. Money — or lack of it — is our big problem here. I think we have two to three more years of survival, but we need this time to find a solution to this," said Simon Greenish, the Trust's director.

As a result of lack of funds, the Trust is unable to rebuild the site's rotting infrastructure and faces an uncertain future. "The Trust is the hardest-up museum I know," said Greenish. "We have this huge estate to run and it's one of the most important World War II stories there is."

Bletchley Park — code-named Station X to keep its location from the Germans — and its outstations were responsible for intercepting German radio signals intended for broadcast to the army, navy and air force, and decoding them into meaningful messages. The job was thought to be next to impossible: German encryption was so secure that the chances of decoding it with random guesses were 150 quintillion to one.

Nine thousand staff worked around the clock at the Buckinghamshire site to break the German codes, eventually gleaning enough information to head off critical enemy manoeuvres.

The operation all started in the mansion pictured above in 1939, when it became the home of the Government Code and Cipher School (GCCS), the forerunner of today's Government Communications Headquarters (GCHQ). 

The government had intervened to prevent a local property tycoon from developing the site for housing, hoping to provide a safer location for the GCCS, away from the obvious dangers of its previous home in central London. At the intersection of major road, rail and telecommunications connections and en route between the top two universities, Cambridge and Oxford, Bletchley Park was ideal.

The intensity of the codebreaking operation meant it soon outgrew the confines of the mansion, spilling into the cottages in the surrounding stable yard.

It was in one of these cottages that the codebreakers first tasted success. Alfred Dillwyn Knox was believed to have broken the first German message in January 1940, five months after the GCCS moved in.

A cryptanalysist and scholar from the University of Cambridge, 55-year-old Knox was critical to Britain's efforts to crack the codes produced by the German Enigma machines.

Sadly, he never survived to see the Allies claim victory, passing away in 1943 while pursuing his codebreaking efforts.

One of the most famous men to have worked at Bletchley Park was Alan Turing, who worked in this wooden hut. The hut, one of eventually a dozen on the site, was rapidly built after the codebreaking efforts overspilled from both the mansion and the surrounding cottages.

Turing is often considered to be the father of modern computing, devising the Turing machine, the Turing test and the Manchester Mark I, one of the world's first recognisable computers.

A Cambridge graduate, Turing was critical to Britain's codebreaking efforts, co-developing the Bombe codebreaking machine that decoded messages from the German Enigma machines.

Turing's hut has been renovated and today hosts a variety of wartime exhibitions. The Bletchley Park Trust has recreated Turing's office at the far end of the hut.

Turing's office would have been one of the more comfortable places to have concentrated on the intensive work at hand, although it would still have been far from luxurious, given the noise and heat produced by the decoding machines.

Some of the work which went on in Turing's hut contributed to the Allied victory in the Battle of the Atlantic. Huge progress was made after German codebooks were retrieved from a U-boat and passed to Turing's codebreakers at Bletchley Park.

Though Turing's hut has been restored to its former glory, most of the remaining huts are deteriorating. Despite the fact that they have listed-building status, due to their historical importance, most of the huts are uninhabitable, including this one, in which codebreakers focused on breaking code sent by the German high command to the army and air force.

"The site is deteriorating; the mansion is crying out; a lot of it is old and decrepit," said Simon Greenish, the Trust's director. "We're having to do something to the mansion roof — it's got 16 leaks just in one part of the roof — but we can't deal with all of that."

The Trust is just about surviving on revenue from its 60,000 annual visitors — entrance to the site costs £10 for an adult — in addition to income from renting out those buildings on the site that remain habitable.

Greenish is also pursuing the possibility of funding from the Department for Culture, Media and Sport and Milton Keynes Council, the local authority.

"This is such an important site. The government is largely responsible for the state it's in anyway, because it's a government site," Greenish said.

Greenish said he is attempting to work around the National Lottery's eligibility criteria for funding and also hopes that Microsoft's founder will come to the site's rescue: "I'm really looking for a personal link to Bill Gates."

In addition to its financial woes, Bletchley Park faces another foe: housing developers.

Ever since the government's early tussles at the start of the war, when it evicted the local property tycoon, Bletchley Park has faced many battles to keep developers at bay.

Two years before Bletchley Park re-opened to the public in the early 1990s, it seemed that its existence was under threat. In 1991, the site was almost empty and plans had been drawn up to redevelop the whole site as a housing development. The site's proximity to Milton Keynes and the M1 made it an attractive prospect for such schemes.

It was only after a highly successful "farewell" party for the site, attended by 400 former codebreakers, and the formation of the Bletchley Park Trust in 1992 that the developers were halted.

Milton Keynes Council declared the site a conservation area in February 1992 and the landowners — the government's land agency and BT — withdrew all planning applications. Seven years later, former Bletchley Park Trust director Christine Large landed a deal with certain developers to secure the future of Bletchley Park in the hands of the Trust.

But some developers remain far from dissuaded, recently winning the right to build houses even closer to the wartime facilities. One of the site's exhibition facilities now rests just 10 yards from 21st-century residential properties.

With giant concrete mixers towering over the edge of the Trust's land, Greenish said he feels the remaining green space between Bletchley Park and surrounding surburbia may be lost, though he plans to fight the advance tooth and nail.

Bletchley Park supplements its income from visitors by hosting a range of conferences and weddings. While many of the wartime huts are rotting, the insides of the Victorian mansion — including the ballroom, billiard room and the library — remain luxurious. A full wedding ceremony and reception in the ballroom (pictured) costs £3,250.

This tiny building, tucked away at the back of the site, was Bletchley Park's secret post office. It served as the mail room for the codebreakers, who could be reached at the undercover address of PO Box 111, London.

Today, the post office of the 1940s has been recreated and runs a business in commemorative and first-day stamps, some of which fetch considerable sums at auction.

A cinema exhibition, housed in this building, is one example of how the Bletchley Park Trust has branched out to widen its appeal. Inside is an exhibition of vintage camera equipment, technical drawings of projectors and old photographs. Visitors can watch wartime-show reels in the 1940s Enigma cinema.

Bletchley Park has its own slice of film heritage tucked away in the mansion's garage.

The widely acclaimed film Enigma, produced in 2001 and starring Dougray Scott and Kate Winslet, featured the Talbot car and ambulance which are now on display in the garage. The 1976 film The Eagle Has Landed, starring Michael Caine, used the two Austins. The vehicles are positioned in a mock 1940s forecourt, showing the price of fuel and the tools used at the time.

Just a short walk from the garage, this scaled-down Mark VII U-boat provides a reminder of German attacks. It was used in the 2001 film Enigma.

Behind it is Hut 12, which the Trust hopes to turn into a new display featuring exhibits on Naval Intelligence Division commander Ian Fleming, of James Bond fame.

Listening stations like these were used to receive the signals intended for Germany's U-boats, army and air force. They were installed in the so-called "Y stations", secret listening posts scattered across the UK and abroad.

The Y stations received the German messages and sent them by teleprinter or motorcycle to Bletchley Park to be decoded and analysed. Many of the teleprinter operators were women, who were drafted in from the Women's Royal Navy Service (WRNS) and the Women's Auxiliary Air Force (WAAF).

This listening station is housed in Bletchley Park's growing National Museum of Computing. The museum is due to be expanded this summer with a display of computers from 1945 up to the present day, including everything from 1960s mainframes to more recent supercomputers.

Some visitors are fortunate enough to receive a tour around the museum from one of Bletchley Park's volunteers, many of whom worked there during the war.

Here is an example of an Enigma machine. The operator would type in the message in plain text, sending electrical impulses through a series of rotating wheels, electrical contacts and wires to produce the enciphered text, which lit up on a panel above the keyboard.

Recipients of the code who knew the settings could enter the enciphered code into another Enigma machine to receive the plain text, letter by letter.

Because of the number of wheels, the chance of decoding a message at random was 150 quintillion to one. This particular model is a four-rotor U-boat machine, from post February 1942, one of eight now stored at Bletchley Park.

This is a reconstructed Bombe, one of the two main British codebreaking machines. It was used to break the codes produced by the German Enigma machines.

Over 200 Bombes were eventually built, based on the expertise of Alan Turing and Gordon Welchman. Turing and Welchman achieved their codebreaking success by recognising several weaknesses in the Germans' communications.

Firstly, the Enigma machines would never encrypt a letter as itself, which markedly reduced the number of permutations. Secondly, the Germans often sent encrypted weather forecasts. Because Bletchley Park could predict the weather, codebreakers could accurately guess the contents of the message and, therefore, the encryption used.

After the war, all the codebreaking machines were destroyed on Winston Churchill's orders so that, in the early years of the Cold War, Russia could not learn of Britain's codebreaking efforts. 

However, thanks to a 12-year rebuild project, based on partial component diagrams recovered from GCHQ, this model is now working and is used today to decode mock enemy messages.

Despite the British starting to crack the Enigma code, Germany had another trick up its sleeve: the Lorenz machine. More complex than the Enigma, the 12-rotor Lorenz was used exclusively for the most important messages between central high command in Berlin and German army field marshals.

It was rather larger than the Enigma and, as a result, not portable. It used the so-called "International Teleprinter Code", with each letter represented by five electrical impulses. Messages were encoded by adding a series of apparently randomly generated letters to the original plain text.

Max Newman, another Cambridge graduate, was assigned the task of building machines to break the Lorenz code.

Newman's answer was the Colossus. His 2,500-valve machine was the first to break the Lorenz code, although Britain had to wait until December 1943 to get the first one installed at Bletchley Park. Nevertheless, that gave time enough to verify that Adolf Hitler had swallowed the D-Day deception campaigns.

A Colossus Mark II was finally reconstructed last autumn after 14 years of work by Tony Sale (pictured). Widely acknowledged as the world's first, practical, electronic, digital, information-processing machine, tape passes through the machine's wheels at a 30 miles per hour, meaning it can read 5,000 characters every second.

When the rebuild was completed, it was pitted in a codebreaking competition against radio enthusiasts who were allowed to employ whatever computing means they had at their disposal. Ironically, Colossus was beaten in the challenge by a German. The competition is due to be repeated in June.

The Typex was Britain's adaptation of the Enigma. It was more secure than its German cousin, boasting five rotors compared to the Enigma's three or four. The technology was eventually combined with the US's equivalent machine to provide inter-Allied communications during the war.

The machine pictured is believed to be the only remaining working Typex machine.

Churchill was keen to provide all the support he could to the codebreakers at Bletchley Park, who he referred to as: "The geese that laid all the golden eggs but never cackled."

In recognition of the former prime minister's support, the site now houses a large collection of Churchill memorabilia, much of it extremely rare, including a life-sized model of him, and a smaller model (pictured) of him posing with the famous "V for Victory" gesture.

Britain owed much of its success in breaking the Enigma code to Polish mathematicians, who managed to reconstruct the Enigma machine and pass on their knowledge.

The Poles had broken the Enigma code as far back as 1932, when the machines were undergoing military trials.

Three of the most outstanding Polish mathematicians — Marian Rejewski, Henryk Zygalski and Jerzy Rozycki — have been commemorated with this memorial next to the cottage where the first Enigma code was broken.

In British eyes, Turing was the ultimate codebreaking hero. His achievements now take pride of place at Bletchley Park in the form of this life-sized statue, made over 18 months from 500,000 slithers of Welsh slate.

The statue shows Turing, in typically scruffy attire, puzzling over an Enigma machine on his desk. The statue was paid for by a foundation set up by the late American philanthropist Sidney Frank, who wanted to recognise the war's unsung heroes.

To donate to the Bletchley Park Trust, please contact the Trust's director, Simon Greenish, or his personal assistant, Sue May, on +44 (0)1908 640404.