Changes to the London congestion charges announced earlier this week by the mayor have left fleet managers in a precarious position of uncertainty.

The changes, which will come into effect on October 27, tie in with the proposed new bands for company car tax that will be announced in March’s Budget.

This means fleets that opt for sub-120g/km cars will save on tax and congestion charges.

“Even if drivers rarely visit the capital, businesses will still benefit from lower taxes and running costs if their drivers choose low-emission cars,” said Mark Sinclair, director of Alphabet.

However, the mayor, Ken Livingstone said the new scheme is “flexible” warning that both the charges and exemptions may be changed in the future, which leaves fleets uncertain about how long the exemption for sub-120g/km car will stay in force.

This means that fleets ordering sub-120g cars in order to allow their drivers to enter London for free may find that in the coming months the changes will be reversed or amended.

This could effectively push the newly exempt cars, such as the BMW 1 Series, back into the charge catchment pool.

Mr Livingstone, who is hoping for re-election in May’s mayoral elections, emphasised that the aim of the charge was still to tackle congestion.

This is despite independent research published last year, which found that the changes will increase the number of vehicles coming into the capital and do little to cut CO2 emissions.

Criticism of the mayor’s new congestion charges has been widespread.

Motor manufacturer and car dealer associations condemned the changes: “It is questionable if the plan will achieve its aim of further reducing central London traffic levels and overall emissions,” said Alec Murray, Chairman of the Retail Motor Industry Federation.

While the chief executive of the Society of Motor Manufacturers and Traders, Paul Everitt said: “This is totally disproportionate and does not present a consistent signal to consumers.”

Sheila Rainger, acting director for the RAC Foundation, agreed, saying the changes will “confuse the public and reduce support and trust for future initiatives”.

She accused the mayor of “political gesturing” ahead of the election.

The BVRLA also added its voice of dissent, saying the mayor’s move was “futile” but will raise revenue “presumably to help fill the hole in the finances of the 2012 Olympics”.

One of the few groups willing to congratulate the mayor was Friends of the Earth saying the move is extremely welcome and supported by most Londoners.