The firm was awarded the Early Contractor Involvement scheme in March 2009 when the scheme had a construction budget of £84m.

Now following extensive design work, Costain confirmed to the Stock Exchange this morning that work is underway on the job with a revised value of £59m.

The length of the new route has also been scaled-back from 5km to 4.5km.

The award from Neath Port Talbot County Borough Council includes construction of 4.5 km of dual carriageway access road from the M4 Junction 38 into Port Talbot and the Docks as well as completing the link to Junction 42 on the M4 and West Wales.

The scheme includes the construction of a bridge over the Swansea to London railway, railway realignment and signalling works and a new main entrance into Port Talbot Tata Steelworks.

Andrew Wyllie, Chief Executive of Costain, said: “We are delighted to have been awarded this contract for Port Talbot which again underlines our position as a market leader in the construction and maintenance of highways in the UK.”