Companies House reports show that the Rock established Kielder Property Management on June 27 last year - less than a month before the profits warning that signalled the start of its crisis. Kielder has one share, owned by Northern Rock, and its three directors are all managers at the bank.

Industry insiders called the arrangement "opportunistic" and unusual, as lenders normally want to avoid appearing to profit from customers' woes.

A Rock spokesman confirmed that Kielder was formed "to hold possession properties to let in the rental market" and that "possession properties can attract a stigma and be valued at less as a result". He added: "Where sale proceeds would be insufficient to repay the [mortgage] loan in full, it is good asset management to purchase and hold the property to let out."

Analysts said the arrangement suggested the Rock was anticipating a large increase in repossessions and planned to buy them at cut price at auction and sell them on through estate agents. They added it was possible that Kielder had been set up to flatter the bank's mortgage provisioning.

One analyst claimed that Kielder could be used to reduce Northern Rock's impairment charge if it was buying properties to ensure that the loans on repossessed homes were repaid "in full". However, he said the impact would be "marginal".

Northern Rock said: "Anything that happened would have been fully and transparently disclosed." It added that customers would also benefit because Kielder would buy the property only if it offered the highest price at auction. In the event, the credit crisis meant that only two properties were bought, it said.