London motorists are set for up to two months of chaos as the world's biggest congestion charging scheme begins today.

Experts have warned that it is almost impossible to measure whether the charge will cut traffic levels because of fluctuations in vehicle speeds due to other factors.

The Telegraph claims mayor Ken Livingstone wants to treble the size of the zone if the scheme is considered to be a success.

Steven Norris, who was unveiled as the Conservative candidate for mayor yesterday, said his immediate priority would be to scrap the charge.

He said: "Congestion charges are absolutely typical of Ken Livingstone; a massive political gesture founded on another unjustified principle, which is to hate people who drive cars."