Work on a renovation project to expand two sections of the M25 orbital motorway in London has started and is expected to cost about £1bn.

The project includes the widening of lanes between junctions 16, 23,27 and 30 from three to four lanes in both directions and also includes refurbishment of the Hatfield tunnel.

Although preliminary work began in May, construction of the 35km section between junctions 16 and 23 began in earnest on the 8 July 2009.

Work on the 26km second section M25 between the M11 and the Dartford River Crossing construction will also start this month.

Connect Plus consortium will make £3.4bn over a 30-year period from the deal by widening 102km of the motorway in total.

The widening work will be completed before the Olympics in 2012.