Mayor Boris Johnson has scrapped plans to increase the central London congestion charge to 25 pounds a day for owners of gas-guzzling cars.

The CO2 charge, brainchild of former London Mayor Ken Livingstone, was due to have come into effect in October.

As well as penalising bigger and faster cars, it would have scrapped the normal eight-pound charge for small, fuel-efficient vehicles.

Critics of the plan had claimed it would have been expensive to implement and might even have increased pollution by allowing thousands of small cars into central London free of charge.

The Conservatives had pledged to scrap the CO2 charge in Johnson's election manifesto. He was elected in May.

Sports car maker Porsche had been challenging Livingstone in the courts and the scrapping of the CO2 charge means its costs will have to be paid by Transport for London.

Porsche said it would donate the costs, which it expected to be a six-figure sum, to Skidz, a charity devoted to taking at-risk youths off the streets and a life of knife crime, and giving them training in mechanical skills and maintenance.

The money has been earmarked for the opening of a new branch of the charity in the western borough of Hillingdon.

Johnson said he was delighted to have been able to scrap the proposed charge.

"I believe the proposal would actually have made congestion worse," he said in a statement.

Peter Hendy, Commissioner of Transport for London, said: "We will be working with the Mayor to strive to cut CO2 emissions from transport in London by promoting cycling and walking, encouraging people to drive in a more efficient way and by cutting Transport for London's own CO2 emissions."

The decision by the Mayor means that the discount for alternative fuel vehicles will remain in place and the existing Congestion Charge scheme, first introduced in 1993, will not be affected.

The London Low Emission Zone, which aims to reduce harmful emissions from the largest diesel-engined vehicles like lorries, buses and coaches, is also unaffected.