From 3 January 2012 the LEZ will expand to include the following vehicles which are registered before January 2002 and do not meet Euro 3 emissions standards: Vans of between 1.205 tonnes and 3.5 tonnes, minibuses of up to 5 tonnes, ambulances and motorcaravans.

Under its ‘Go Green and Clean Allowance’, which will run from 1 May 2011 to 31 March 2012, Citroen will offer savings of £1750 towards a new Nemo in exchange for an old van,  £2500 for a Berlingo or a Dispatch Combi and £3500 for a Dispatch LCV or Relay.

In order to qualify for the scheme, operators must be able to prove that their old vans are taxed, MOTed and roadworthy so that dealers can dispose of them at auction or to buyers operating outside of London.

As a spokesman for Citroen put it, the allowance will not cover “old snodgers”.

“The vehicle must still have some value,” he said.

Crucially, to get a discount on a new van, customers must produce the letter from Transport for London (TfL) informing them of their obligation to pay a daily charge of £100 to use their existing van within the LEZ. TfL will send out letters to the registered keepers of affected vehicles in April.

London mayor Boris Johnson (pictured) has endorsed the scheme.