Vince Cable, the liberal democrat’s treasury spokesperson, has shown a lack of understanding the public sector IT market in his demands that several major programmes should be scrapped, according to a leading analyst in the field.

In a television interview with the BBC today Vince Cable laid out his party’s plans for cost cutting across the public sector especially focusing on public sector IT. Stephen Roberts, principal analyst at public sector IT specialist Kable, says the Liberal Democrat shadow chancellor has greatly exaggerated the scope for savings and failed to explain how some would be made.

"It's hard to see how he has arrived at some of these projections, and he seems to have fallen into tilting at the usual set of government IT windmills without questioning whether they are appropriate targets," Roberts says.

Among Cable's proposals to reduce public sector spending - made in his report Tackling the Fiscal Crisis - are that the government should drop the national identity card, the ContactPoint children's database, and the "super database" in the Interception Modernisation Programme. He also calls for sharp cuts in England's NHS IT programme, claiming it has been costed at £18bn-£20bn.

Roberts says that several of the figures quoted are unreliable, and the assertions attached are often vague. "The costs of the Interception Modernisation Programme are generally estimated at £2bn, not £6bn. And the communications providers will be expected to hold data themselves: Clegg's "super database" is no more real than Cameron's "NHS supercomputer". The estimates of £20bn each for the NHS IT Programme and for ID cards are out of step with all government and independent forecasts. "

Cable also claims that a move towards using more open source technology in UK government would save up to £500m per year. Roberts says that public bodies are already able to choose open source for many applications, and that the savings figure is implausible.

"He's suggesting that costs for software could be reduced by almost half. There's a surprising amount of open source software in government already, and there isn't an open source alternative for much of the proprietary software used, so that's hugely ambitious."