Like many large organizations around the world, London's Met has been paying for Microsoft Custom Support Agreement in order to continue receiving security updates for the operating system, which Microsoft stopped patching for free in April 2014.
In April last year, the Met revealed to Motherboard that it had some 35,000 Windows XP machines under this support arrangement. Since then, the Met has upgraded 8,000 PCs to Windows 8.1, but Conservative Greater London Assembly member Andrew Boff has raised concerns that 27,000 PCs are still running the ageing system.
"The Met should have stopped using Windows XP in 2014 when extended support ended, and to hear that 27,000 computers are still using it is worrying," Boff said in a statement.
"My major concern is the security of Londoners' information on this dangerously out of date system, but I would also like to know how much money the Met have wasted on bespoke security updates."
Boff, a former IT consultant, also questioned why the Met was migrating to Windows 8.1 rather than the newer, more secure Windows 10.
"Windows 8.1... is neither the newest version of Windows nor the most used version of the software. Staff are likely to be more familiar with Windows 10, but most importantly it will be supported further into the future," he said.
According to the BBC, the Met has a £1.65m ($2.15m) deal with Microsoft for continued Windows XP support until April 2017.
The police force is currently planning to move a further 6,000 desktops to Windows 8.1 by the end of September.
In other words, it's taken the Met over a year to migrate 8,000 desktops off Windows XP, and it now may need to move 21,000 desktops off Windows XP within eight months.
However, not all those devices will be migrated. The Met told the BBC that it was developing alternative plans for the remaining XP desktops, including disposing of equipment that can't support Windows 8.1 and beyond. It said the reason it was still migrating off XP was due to legacy software.
The Met is not alone in coughing up taxpayer dollars for continued Windows XP support. The US Navy last year agreed to pay Microsoft at least $9m for Windows XP support until July 2016, with a $31m option to extend the deal until June 2017 if necessary.
Australia's Department of Finance revealed earlier this year that it is paying Microsoft $3.4m for whole-of-government Windows XP support through to July 2017, according to iTNews.