Only buses, coaches and taxis can use the lane which runs on a section of the motorway between Heathrow airport and central London.

Speed limits have also been reduced from 70mph to 50mph along the two remaining lanes.

But journey times have improved for all types of traffic in the first three months of the operation of the £1.9m lane on the M4 in west London, according to Transport Research Laboratory figures.

The figures will delight Mr Prescott, who was pictured against a backdrop of huge jams when the 3.5 mile-long lane was introduced on a one-year trial basis in June 1999.

He has also come under severe criticism for failing to get to grips with the UK's transport problems.

Blair 'cheated'

Shortly after the lane was opened, it was reported that Tony Blair's car had "cheated" and used the lane when the prime minister got stuck in a jam while heading for London.

Shadow environment secretary John Redwood called for the bus lane to be scrapped, saying that he, like many motorists, he had spent "many unhappy minutes" in traffic staring at the empty lane and "waiting to see the prime minister sweep by".

Figures published by the Highways Agency for the first three months of the scheme show: