Costain and May Gurney have announced merger plans.
The companies will have combined revenues of £1.6 billion and challenge rivals including Balfour Beatty and Carillion.
Major infrastructure contractor Costain, which is working on London's Crossrail underground rail tunnel, is based in Maidenhead, which will be the group's headquarters.
The group plans to retain May Gurney's headquarters in Trowse, Norwich, as a shared services base.
May Gurney has around 800 of its workforce in Norfolk.
More top news
We're one week into December and the countdown to Christmas is well underway. Read the latest in ITV News Anglia's Christmas Shout Outs.
The grandparents of missing serviceman Corrie McKeague have travelled 425 miles from their home in Scotland to retrace his last steps.
A dry night with broken cloud and occasional clear spells. Generally cloudy with occasional outbreaks of rain during Thursday morning.