The carriers will be assembled at Rosyth shipyards

Mr Darling has told MPs the �4bn carriers will be assembled at Govan and Rosyth in Scotland, as well as in Tyneside and Portsmouth.

He said those sites had been chosen subject to "value for money" tests.

The two 950ft long, 60,000-tonne carriers will be the biggest British warships ever built.

The value of the work is likely to rise to �10bn when maintenance and support is added.

On Monday, Kellogg Brown and Root (KBR), a subsidiary of US firm Halliburton, won the contract to manage the construction of the ships.

Campaign

It had been reported that KBR was planning to have the ships built at Nigg, on the north-eastern coast of Scotland.

However unions and MPs, including Chancellor Gordon Brown, campaigned for construction to take place at Rosyth to protect local jobs.

BAE's yards are manufacturing sections of the carriers

In the Commons on Tuesday, Mr Darling was asked Nigg's MP John Thurso, for assurances that the sites would be chosen according to which gave the best value "and not, as the press suggested, a fix for the Treasury".

Mr Darling said: "We anticipate that, subject to value for money, the carriers will be built potentially at four sites in the UK - at Govan, Portsmouth, Tyneside and Rosyth.

"It will be subject to value for money."

BAE systems and the French firm Thales have won contracts to build the ships in sections.

These will then be floated to Rosyth where KBR will oversee their assembly.

In a written statement, Defence Secretary Geoff Hoon said the project would create or safeguard 10,000 jobs.