Taxi drivers have failed in a High Court bid to reverse a decision forcing them to fit "faulty" exhaust filters.
Since last July drivers of 15,000 London black cabs have been required to fit systems to limit nitrogen oxide and diesel soot emissions from their cabs.
But the London Cab Drivers Club said the filters do not work at the low speeds they usually drive in the city.
A deputy High Court judge rejected their application, ruling that the challenge was "doomed to failure".
Transport for London and licensing authority the Public Carriage Office introduced the change last year.
As a result the drivers said they each had to pay £1,900 to have the filter equipment fitted to their vehicles, but quickly found that it did not work.
They were then forced to modify the kit, costing a further £400, but the filters still clogged and their vehicles gave out black smoke as a result.
Rejecting the challenge, Judge Mole ruled: "As long as the decision maker is satisfied at the end of the process that the system is going to work, the decision is wholly rational and completely beyond challenge."
Outside court, London mayor Ken Livingstone said the decision was "a great victory in the effort to clean up London's environment by tackling pollution".
He added: "The London Cab Drivers' Club are a small, unrepresentative group of taxi drivers who have long been opposed to my strategy to improve London's air quality."
However club chairman Alan Fleming said: "The cab trade is not opposed to the idea of achieving a clean-up of London's air quality because we have to sit in it all day long.
"But if we are going to have to spend this money we want to be confident that what we are buying is actually working. What we have is a waste of money and a waste of time."