When DML won the contract, the cost was estimated at �650m

Representatives from the dockyard and the Ministry of Defence (MoD) were questioned by MPs about the cost of the project to build new facilities at Devonport for nuclear submarines.

MPs on the Public Accounts Committee were following up a report from the National Audit Office that revealed Devonport Management Limited (DML), the firm which manages the yard, had originally estimated the cost of work would be �650m.

The bill is now �933m - an increase of 31%.

Devonport 1980: Purpose-built nuclear submarine refit complex opened 330 acres 11 dry docks Base for seven nuclear-powered submarines

Sir Kevin Tebbit, the MoD representative, said the extra money was necessary to ensure safety standards and maintain Britain's nuclear deterrent.

On Monday, the committee said the whole project had been a "monumental failure".

But DML Chairman Tony Prior disagreed.

He said it was an "outstanding achievement" because the project, the biggest construction project in Europe at the time, was delivered on time.

Most of the cost-overrun is being paid for by the MoD but DML is making a loss of �43m.

It was supposed to make �30m profit.

But DML denies that its losses will lead to job losses.

It says that the 240 job losses announced in January are unrelated to the over-spend.