The Enquirer understands that a decision is due within weeks on a winner between bids involving Balfour Beatty, Laing O’Rourke and Costain.

Balfour is working with Vinci on its bid, O’Rourke alongside Bouygues and Costain with Sir Robert McAlpine and Hochtief.

The huge civils contract will employ at least 1,500 construction workers and take more than three years with a start on site due early 2013.

Chairman Ray O’Rourke is leading the O’Rourke bidding team and has had a series of recent meetings with client EDF.

Sources close to the talks said O’Rourke’s large directly employed workforce could be the deciding factor in the negotiations.

The source told the Enquirer: “The others just can’t compete in terms of a directly employed site workforce and that could be a crucial factor.

“O’Rourke’s industrial relations record on sites like the Olympics will also be crucial.

“A decision on the preferred bidder is only weeks away and the feeling is that the job is O’Rourke’s to lose.”

An EDF sokesman said: “We do not comment on contract awards while the process is live.”