The Bank of England told Alistair Darling, the Chancellor, that only he could support a secret takeover approach that might have saved Northern Rock, days before the run on the mortgage lender, it emerged last night.

Mervyn King, the Bank’s Governor, has shed light on the tentative approach for Northern Rock from Lloyds TSB. The bid broke down in early September after Lloyds asked for a £30 billion Bank loan at competitive rates as part of the deal.

In an interview to be broadcast tonight on BBC Radio 4’s File on 4, Mr King said: “I said to the Chancellor: ‘Well look, this is not something which a central bank can do, they don’t normally fund takeovers by one company for another, let alone to the tune of £30 billion, which is rather a large amount of money.’ ”

“So I said: ‘This is a matter for government, but you have to recognise that if you were to make available such a facility to one bank, you would have to make it available to any other potential bidder and therefore it will become public.’

“And I don’t think it took the Chancellor very long to recognise that not only was this something which central banks don’t do, it’s also something that governments don’t do.”

A Treasury spokesman said that the Lloyds proposal had never been a substantive bid and the suggestion of a loan was only a general inquiry.

Meanwhile, Northern Rock has seen a dramatic fall in mortgage lending since its problems emerged, according to Charcol, the mortgage broker. Charcol estimates that the lender has been doing about 20 per cent of the business it was doing before the start of the summer.

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