Lenders are facing a regulatory crackdown as the Bank of England prepares to pop the London housing bubble, with Barclays and Santander among those that could see lending curbed, according to a leading mortgage market expert.

Speculation is also mounting that Royal Bank of Scotland, which is 80 per cent owned by the State, will be next to announce voluntary curbs after Lloyds Banking Group last week toughened its lending terms in London. Lloyds, which is 25 per cent State-owned, said that it would restrict London borrowers looking for loans of more than £500,000 to four times their salary.

Lloyds insists the move was based on deep research and suspicions of a bubble in prices, but Ray Boulger of mortgage broker John Charcol said the Lloyds announcement had “all the signs of being political”, adding fuel to speculation that RBS, which owns NatWest, would also take voluntary steps before any action is imposed.

He also identified Santander, Clydesdale Bank and Barclays subsidiary Woolwich as the biggest providers of new mortgages, including interest-only loans, in the high-end London market.

Sources denied that the Bank of England had put pressure on Lloyds, which insisted it had made a normal commercial decision — but there was speculation that the bank would please the Chancellor by appearing to take the heat out of the politically contentious London market.

There was speculation last week that NatWest, through which RBS advances many of its London home loans, would be next to restrict lending in the capital. RBS declined to comment, but a source did say that it was “continually looking at whether it is necessary to do anything similar to Lloyds”.

Boulger said that Lloyds alone would be unlikely to knock the market. “If we got RBS and another lender, that starts to put pressure on other lenders,” he said.

The Bank of England’s Financial Policy Committee, which is in charge of the stability of the financial system, meets on June 17 and is expected to discuss using its powers to tame the wilder extremes of the housing market, notably London, where average prices are rising at 18 per cent a year. The powers are a key alternative to interest rate rises as a way to control housing bubbles.

— Mail On Sunday