The UK government has "no clear plan" for how to replace legacy IT systems that form the backbone of public sector services.

The Parliamentary Public Accounts Committee said that the aging equipment could break, and represented a security risk.

"Many of these systems are stable and performing acceptably at reasonable cost, but others are high risk, unreliable, contain security vulnerabilities, or frustrate business transformation," a report by the committee, first spotted by The Register, notes.

In September, the National Audit Office disclosed that a 34-year-old ICL mainframe system was one of the reasons that more than £1 billion ($1.3bn) of state pensions were not paid.

"The Emergency Services Network and Digital Services at the Border programmes are examples of critical projects which have suffered from severe delays and cost overruns, this latest project does not give the committee any comfort that the Department is learning from past mistakes," the PAC said.

"Over the last five years, the Department has wasted both vital time and scarce funding without making any meaningful progress in replacing the Police National Computer (PNC) and the Police National Database (PND)," the committee said.

It added that a replacement to the PNC is expected to be at least five years late, and cost 68 percent more than planned.

Last year, tax body HMRC said that - despite plans to shift off of legacy IT seven years ago - it still had no end date for its 26-year-old systems.

A July report by the Modernisation and Reform group found that £2.3bn of the £4.7bn the UK government spent on IT in 2019 was on supporting "outdated legacy systems." Between £13bn to £22bn was expected to be spent over the next five years.