A construction plan to build 35km between junctions 16 and 23 has been officially started by the UK’s transport minister Sadiq Khan.

As part of the plan the £6.2bn design, build, finance and operate contract has been awarded to the Connect Plus consortium.

As part of the contract, two sections of London’s orbital motorway between junctions 16 and 23 in the north west and between junctions 27 and 30 in the north east will be widened to four lanes from three in both directions.

Refurbishment of the Hatfield Tunnel will also be carried out as part of the contract.

Work to widen the 26km second section of the M25 between the M11 and the Dartford River Crossing is also set to begin this month.

The road widening will increase the capacity on the busiest sections of motorways and trunk roads.

The construction phase would employ between 3,500 and 4,000 people until 2012 in addition to around 850 people employed on the 30-year operations and maintenance work.

The Connect Plus consortium is expected to make £3.4bn over a 30-year period from the deal to widen 102km of the motorway in total.

All the widening work is due to be completed before the Olympics in 2012.