Northern Rock has begun offering mortgages to existing customers again — for the first time since the bank was nationalised in 2007. The move comes as the government prepares Northern Rock for a possible sale as early as the autumn.

Customers coming to the end of discounted deals are being quietly offered new mortgages if they have 25% equity in their home and satisfy “strict affordability criteria”.

Existing customers do not need to have their property revalued.

Northern Rock is considering extending the scheme to those who need to borrow 90% of the value of their property.

Mortgage experts said the bank wanted to improve the quality of its loan book to make it more attractive to bidders. The rates on offer are better than those for new borrowers, inducing customers to stay with Northern Rock.

A number of colourful bidders for the bank are already emerging, but the one that may ruffle a few feathers in Westminster is Pamplona Capital, the private equity firm founded by Russian oligarch billionaire Alex Knaster, who sits on the board of BP’s contentious Russian joint venture, TNK-BP.

Virgin’s Sir Richard Branson and billionaire US financier Wilbur Ross are expected to bid jointly.

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