The Electricity Alliance West framework contract is estimated to be worth up to £650m. It will see the joint venture continue to provide design engineering, programme management and construction services through to March 2017.

Babcock and AMEC are majority partners working with Mott MacDonald.

Balfour Beatty has also signed a five-year contact extension worth around £750m under the Electricity Alliance East partnership with National Grid.

Peter Boreham, UK Construction Director for National Grid said: “In the period up to 2021, National Grid expects to invest around £20bn in our gas and electricity transmission infrastructure to support the UK’s growing energy needs.

“Our Construction Division has a major role to play in supporting this unprecedented level of growth and the continuation of our alliance partnerships will play a pivotal role in successfully delivering that forecasted increase, with a continued focus on delivering our work safely, efficiently and sustainably.”

Peter Rogers, chief executive of Babcock, said: “We are delighted that our long standing customer National Grid has extended our existing contract, which reflects the excellent performance of the Alliance over the past five years.

“We look forward to building on this partnership with National Grid as it delivers the significant investment programme required to support the UK’s growing energy needs.”