Sir Peter Gershon, the businessman who drew up Whitehall's £21 billion efficiency savings programme, described the Tory plans to cut £35 billion by 2008 as "undeliverable in the timescale without legislation".

Speaking to MPs on the Commons public administration committee, Gershon said that managing government efficiency and savings was much more complex than in the private sector.

"Government is not like Tescos; it is not a simple command-and-control structure between head office and an individual supermarket," he said.