Ken Livingstone is facing a full-scale legal challenge to his plan to charge gas-guzzling cars £25 day in congestion charging.

Porsche is writing to the London Mayor claiming his new scheme - unveiled last week - is "unjust" and says he must axe it or face a judicial review.

It says that the increase - a 3,025 per cent rise for central London residents driving the biggest polluters - is disproportionate.

And it claims Mr Livingstone's plans will do almost nothing to achieve his stated aim of decreasing vehicle emissions.

Today, Porsche Cars GB managing director Andy Goss said Mr Livingstone had 14 days to respond to its letter, sent this week.

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He added: "If the Mayor fails to respond to Porsche's letter or refuses to reconsider his plans, Porsche intends formally to submit its application for judicial review at the Royal Courts of Justice."

If the courts give the review the go-ahead, Porsche will challenge Transport for London's right to launch the emissions-related congestion charge - which is due to start in October if Mr Livingstone is re-elected.

Porsche said it would seek a "quashing order" that, if granted, would overturn the new charge.

Mr Goss added: "A massive congestion charge increase is quite simply unjust.

"Thousands of car owners will be hit by a disproportionate tax which will have a very limited effect on CO2 emissions.

"Not only is this rise completely unfair to many drivers but it will also damage London based-businesses of all sizes, and successful people from across the world will start to think twice about basing themselves here if they think they are going to be used as cash cows for City Hall."

Under the Mayor's plans, which include a 100 per cent discount for cleaner small-engined cars, the congestion charge will rise from £8 to £25 - by 213 per cent - for vehicles that emit more than 225g of CO2 per km.

Full article here.