The Metropolitan Police Service (MPS) has admitted that a "complete refresh" of its internal computer systems is taking longer than expected, with just under 20,000 desktops still running 15-year-old Windows XP software.

In a statement to IBTimes UK, a Met Police spokesperson confirmed that roughly 19,500 desktop computers are currently running XP – a reduction of 7,500 from the 27,000 systems that relied on the operating system at last count in August.

"The MPS is undergoing a complete refresh of its information technology processes [...] including its desktop computers," a statement read.

"However, the upgrade programme is not as simple as it would be for other organisations due to the amount of specialist legacy software upon which parts of the MPS still rely."

The Met said plans are now being developed to "address the remaining XP desktops" and that the aim will be to reduce the overall number used by the police in favour of devices such as laptops and tablets. Technology that can't support Windows 8.1 will be disposed with, it added.

Microsoft stopped releasing official security updates for XP back in April 2014 however organisations can continue to receive security updates by paying Microsoft for the additional support. According to the Met this has cost £1.65m to date. "We have no security concerns," the spokesperson claimed.

The Met has a so-called extended support agreement running until April 2017 however an exact time-scale for the refresh is yet to be finalised. "At this stage we cannot give a date for the completion of this programme, but it is being progressed as rapidly as is possible," it said.

London Assembly Member Andrew Boff has previously criticised the slow pace of computer upgrades and said the outdated software could potentially put data at risk of hacking.

"Windows XP is well past its sell-by date," he said in August. "The Met should have stopped using Windows XP in 2014 when support ended. My major concern is the security of Londoners' information on this dangerously out-of-date system.

"I also question the choice to upgrade to Windows 8.1; this is neither the newest nor the most used version of Windows. Staff are likely to be more familiar with Windows 10, but most importantly it will be supported further into the future."

Just prior to official support being cut off in 2014 it was revealed the Met had 35,000 computers still running Windows XP. At the time, through a modernisation programme, the police set an initial deadline of March 2016 to make the jump to Windows 8.1.

Additional source: V3.co.uk