The extra work windfall compensates for agreed changes to the scope of work with the anticipated extra spend in line with the HS2 budget.
The total contract, valued at £1.2bn, involves the design and construction of major tunnels in the approach to the London terminus at Euston station.
The twin bored tunnel will be 13 miles each way and, with a combined total of 26 miles, the same length as the Elizabeth Line project.
Since being given notice to proceed by HS2 in April 2020, significant progress has been made on the project.
This includes major earthworks, operations to assemble the first tunnel boring machine for launch this summer at the Old Oak Common site and the building of major structures, such as a new rail transportation logistics hub that will remove one million lorry journeys from London’s roads.
In total 3,500 people are currently working on this section of the project.