William Hague will sack one in 10 civil servants if the Conservatives win the next election.

The Conservatives will unveil plans for a massive overhaul of ministerial posts and government departments at the party's spring conference in Harrogate as part of their "Blueprint for government".

Hague believes that a rationalisation programme across Whitehall, including the abolition of three ministerial cabinet posts, would raise £1.8 billion for tax cuts. The initiative, together with the privatisation of Channel 4, would form the bulk of the £8 billion that Hague and his shadow chancellor have promised to deliver.

The Tory leader has already discussed the scheme with cabinet secretary Sir Richard Wilson at the traditional pre-poll meeting where he revealed his party's election plans to Whitehall chiefs.

The union representing senior civil servants dismissed the plans as a re-announcement and said the scheme was unworkable.

Jonathan Baume, general secretary of the First Division Civil Servants Association said: "This is not a new idea from the Conservatives. Government departments are already extremely stretched with employees already working long hours. Senior politicians must recognise that civil servants deliver a wide range of public services. Cut civil servants and you cut services."

He denied Labour had increased the number of civil servants. "The present government employs 475,000 civil servants, exactly the same number as when John Major left office. Labour did cut the overall total but has recently had to recruit extra staff, to, for example, speed up consideration of immigration and asylum cases and because of a rise in the prison population," he said.

Baume said the job cuts would affect Conservative plans to find other savings. "You cannot fight benefit fraud and at the same time cut the number of fraud inspectors. And there would be increased government revenues if more staff were hired to fight tax non-compliance and widespread smuggling, particularly of cigarettes and alcohol."

"The FDA is not entering the pre-election battle between Labour and Conservative, but if politicians demand cuts in the civil service they must be honest and explain where those cuts will come from. Otherwise the voter is being conned," he said.