In the chancellor’s pre-Budget report on Wednesday, Gordon Brown will boast of the government’s success in its Gershon efficiency review – but the billions of claimed savings will be the subject of intense debate.

There will be the usual battery of statistics and examples to illustrate the government’s claim that, exactly halfway through the three-year exercise, departments have already achieved more than half the planned savings – £13.3bn out of the £21.4bn due by April 2008.