Britain's largest union is welcoming the intervention of London Mayor, Boris Johnson, in support of its campaign to keep production of the UK capital's TX4 black cab in domestic hands.

The Unite labour body wrote to UK Prime Minister, David Cameron, Business Secretary, Vince Cable, Transport Secretary, Patrick McLoughlin and Johnson, urging them to support its 'Save the Black Cab' campaign and has received enthusiastic support from the London Mayor.

The TX4 cab manufacturer, Manganese Bronze, is currently in administration, after it was hit by a recall following problems with steering boxes supplied from China, with PricewaterhouseCoopers evaluating bids that could total as many as 50 for the producer.

"Be in no doubt I remain fully committed to the future of the iconic black taxi and will do everything in my power to help ensure a secure future for cab drivers in London," said Johnson in his reply to Unite.

"Please take this letter as proof of my support for your campaign to keep the black cab on the streets."

Unite - with 1,000 black cab drivers among London's 26,000-strong total - added there was now a "very real risk" the company could collapse or that the taxi could end up being built abroad.

"People are concerned there may be problems in the sale potentially and what we want to see is a company in the UK," a Unite spokesman told just-auto.

"Boris Johnson has written to us to confirm he supports our campaign and we welcome that. What we want to see happen is for this process deciding who might potentially buy Manganese Bronze, that it does not take place in the dark."

Unite says the administrators are reaching "a crucial stage" in short-listing potential buyers and is urging stakeholders to apply as much pressure as possible to ensure any purchaser commits to building the black cabs in the UK.

"Unite is urging PWC and any potential buyer to keep manufacturing in Coventry and the black cab on the road," said the union.

"PWC could make the final decision on the company's future towards the end of  this month or early January."

The Licensed Taxi Drivers Association in London was not immediately available for comment.