Lender Abbey said it has claimed more than a fifth of a shrunken mortgage market between July and September as it filled the gap left by struggling rivals.
The group's gross lending of £19bn represented 20.5% of the market - well above its historic 13.4% share - although the figure was 37% down on the previous year.
Spanish-owned Abbey said new mortgage lending of £5.1bn - overall lending less repayments - represented more than half the estimated market size.
The group has two million mortgage customers and also owns Alliance & Leicester and the savings business of Bradford & Bingley. It lifted pre-tax profits by more than 30% to £1.16bn in the third quarter of 2009.
Bad debt provisions are rising but at a lower than expected rate due to the quality of the loan book and record low interest rates.
Chief executive Antonio Horta-Osorio said: “Our strategy of offering value-for-money products, underpinned by responsible lending and controlled costs, has seen us deliver a significant uplift in revenues and allowed us to continue to support the UK economy with increased lending to homeowners and businesses.”
The business also has around 15 million savers following its moves for A&L and B&B last year - taking in £2.7bn in retail deposits so far this year.
The bank has also boosted its share of current accounts by more than 20% so far this year and is on track to open one million new accounts by the end of 2009.