Prestel's claim was made on the back of an independent study by BDO Stoy Hayward, measuring the access speeds of six big-name ISPs. The other five comprised AOL, BT, CompuServe, Demon and Pipex.
The data shows Prestel's rivals averaging 58 per cent slower performance and awarded only AOL and Prestel with 100 per cent connect and download success rates. Prestel claims that the results show the firm's wisdom in going for raw speed by employing the latest hardware.
"Users of other ISPs are still surfing on outmoded copper," a spokesman said.
The results are based on tests recorded three times a day, timing how long a 1.25Mb file and a 2.4Mb file took to download from the Microsoft and Netscape Web sites respectively. Six PCs were used, with telephone lines and PCs alternated to establish a level playing field.
"It may be a little invalid," said Alan Scott, business development group manager at CompuServe UK. "We launched a new PoP [point of presence] providing 28,800bps dedicated Internet access across the UK just four days ago. It's such a dynamic market with ISPs constantly updating speeds that these tests are probably out of date already. We'll have 57,600bps inside a month and a new PPP [point-to-point protocol] farm, so we're pretty sure we've got a fast network."
Scott said new benchmarks that attempt to measure real-world ISP performance will have to be carefully written.
"There are so many variables concerning amount of usage, different servers and so on, that it's very difficult to establish which are the fastest."
"They're claims - my Dad is bigger than you're Dad," said David Barrett, head of corporate communications at Pipex. "We've got 33,600bps Internet access in terms of dial-up which, as far as I know, is the fastest pan-UK service. Prestel isn't a service we come across much. If you launch a service with five modems tomorrow and hardly anybody knew, you could be very fast.
"Also, it's misleading to look only at dial-up; the vast majority of Internet access is via a corporate LAN so by definition they're taking a very small section of the marketplace."