Nationwide underlying profit surged 27 percent
Gross mortgage lending rose 14% to £14.9bn, representing 13.2% of the UK market.
"This has been our best ever half year of mortgage lending along with a strong inflow of savings and the opening of over a quarter of a million new current accounts," said chief executive Graham Beale.
"Mutuals, like Nationwide, are different from the banks. Nationwide is evidence that you can be successful by doing the right thing."
However, the building society warned "robust" competition would lead to strong "downward pressure" on its profit margins in the second half of the year.
Beale added the UK housing market remained "healthy and strong" and forecast house inflation to continue at about 3% to 4%, although he expected a cool-down phase in the London property market.
"My expectation is you will see a dampening of prices in London as there comes a point when it the price overwhelms the growth in wages." ■