From Tuesday 18 April a taxi presented at the Public Carriage Office (PCO) for its annual inspection will already have to have passed an instrumented smoke test on its exhaust.
This test will be carried out at MOT garages equipped for testing diesel cars. Garages will be able to charge a fee for the test.
'We have known for some time that taxis are perceived as amongst the highest contributors to visible environmental pollution in London,' Mr Norris said.
'The introduction of the test is in line with the government's policy that all diesel-engine cars should undergo annual testing to ensure that exhaust emissions are kept to a minimum.'
When a taxi passes an instrumented smoke test, the owner will be given a certificate which will have to be given to the PCO. These certificates will be valid for 28 days, so that should the taxi fail the PCO inspection for any other reason, it will not necessarily have to have its exhaust retested.
If a cab is presented to the PCO with a smoky exhaust, the PCO will not license the cab even though it has a smoke certificate. The owner will be required to rectify the fault before the PCO will consider licensing the vehicle.
Taxis outside London have been subject to the instrumented smoke test as part of the MOT test since 1 February 1994.