An official announcement is expected next week after Costain/Skanska edged ahead of its rivals.
The deal would see the joint venture beat consortiums of Balfour Beatty, Morgan Sindall and Vinci, Bam Nuttall, Ferrovial Agroman and Kier Construction, Laing O’Rourke and Strabag JV and Carillion.
Work is due to start in October on the highly complex engineering task which will see the station take the form of a 230m long underground box, 23m below the existing taxi concourse at Eastbourne Terrace on the south side of the famous Grade 1 listed Brunel station.