Westpac management has insisted that its push for growth in the mortgage, business loan, personal loan and credit card markets will not be at the cost of margin or credit quality.Westpac's group executive for retail and business banking, Jason Yetton, told analysts at a briefing on Friday that the bank shifted its emphasis from strengthening the balance sheet to growing assets in the middle of last year.The bank increased its "share of voice" with more advertising, it added 80 home lenders, beefed up its training programs and gave lenders more credit authority.The result was a 29 per cent increase in mortgage approvals in the December 2013 quarter, compared with the same quarter in 2012. Credit card applications rose 62 per cent in the five months to November.Business lending in the December quarter was up six per cent on the previous corresponding period.Having lagged behind the rest of the industry in mortgage sales throughout 2013, Westpac is now close to matching system growth.Yetton said the bank had achieved this growth without increasing its risk appetite. He said the bank had not increased the average loan-to-valuation ratio of new loans and customers' credit scores had actually increased slightly.On the question of margins, he said the bank had matched the industry average by adding another 10 basis points to its home loan package discounts but higher margins on deposits meant that it was not sacrificing net interest margin to achieve growth.The bank revealed just how much of a problem prepayment run-off was at the moment, with borrowers taking advantage of low interest rates to accelerate repayments on their loans.In the December quarter of 2012 new mortgage lending was A$11.7 billion, while run-off was $9.3 billion. In the March quarter last year new lending was $14.7 billion and run-off was $10.5 billion. In the June quarter new lending was $14.9 billion and run-off was $12.4 billion. And in the September quarter new lending was $17.8 billion and run-off was $13 billion.Yetton said: "We have looked at what triggers run-off so we can be more proactive with customers. Those triggers include the age of the loan, a change in valuation of the property and fixed rate loans maturing."One interesting disclosure was that 43 per cent of Westpac's mortgage customers are investors. With the pick-up in housing finance being led by investors last year, Westpac has been one of the main beneficiaries.