Workers at Devonport rejoiced in 1993 when the dockyard was awarded the contract to refit Britain's Trident nuclear submarines.

Now Devonport has been left acutely embarassed after the National Audit Office (NAO) revealed that costs of refitting the yard for the subs has ballooned from �650m to �933m.

The MoD is blaming the private contractor building the facility, Devonport Management Limited (DML), and DML is blaming the MoD.

But the revelations have also reopened old wounds about why the contract was awarded to Devonport in the first place.

Devonport gives a very big boost to the Plymouth economy, and it really does need it

Professor Peter Gripaios

Rosyth, where Chancellor Gordon Brown is MP, was shocked when the then Conservative government said that the job would go out to tender.

Rosyth had already splashed out �110m on preparations for the work.

And it claimed that it had been promised the contract.

In the end Devonport won by undercutting Rosyth by �11m - a figure that looks paltry compared to the overspending just revealed.

Many Scottish MPs accused the government of cynically trying to woo West Country voters.

But while Devonport and Rosyth were at loggerheads, both sides agreed on one thing - the huge economic benefits that the work would bring.

Economic lynchpin

It was estimated that 20,000 jobs would be lost and the local economy would nosedive if Devonport failed to win the contract.

The �1bn refits of Trident subs over the next decade will keep half of DML's 4,000-strong staff in work.

Plymouth University economics professor Peter Gripaios said that income from Devonport is still of huge value to the area.

He said: "The effect of this spending is pretty widespread across Devon and Cornwall, although most of it is in Plymouth itself.

"It gives a very big boost to the Plymouth economy, and it really does need it.

"It is really suffering on other fronts. Many call centres are going and many of the manufacturers are facing difficulties, so the longer that this work carries on, the better for the city."

Meanwhile, work is continuing at the dockyard on the modernisation programme which will allow the second of the four Trident submarines to be refitted.

And the NAO report warns that a number of "critical facilities" still need to be completed for HMS Vanguard to leave on time after its two-year refit.