Residential mortgage gross lending stood at £5.0bn, compared to £5.7bn in Q1 2014.
It saw a small fall in mortgage balances from £150.1bn in Q4 2014 to £149.7bn at the end of March, which it attributed to "weak application volumes in Q4 2014".
SVR mortgage loan balances fell £2.1bn to £41.8bn, although the bank successfully retained 35,000 customers (80%) with maturing products on Santander UK mortgages.
Santander maintained an average LTV of 65% on new lending, including Help to Buy, and 47% on the stock of mortgages.
Help to Buy comprised all of the lending with an LTV over 90%, with demand higher than expected since its inception. Excluding Help to Buy, the average LTV on new lending was 64%, and lending with an LTV of over 85% accounted for 18% of the new business flow, of which 15% was Help to Buy.
In total, it has helped 6,900 first-time buyers (£990m of gross lending) and 1,100 Help to Buy customers (£148m) purchase a home.
Overall, profit before tax was up 13%, rising to £470m from £416m in Q1 2014.
Nathan Bostock, Chief Executive Officer, said:
“I am pleased to report a good start to the year. We have seen further improvement in customer satisfaction and a continued increase in profitability.
"The UK economy continues to be supportive of our business in 2015. We await further clarification on the regulatory landscape this year, in relation to capital, leverage, conduct and banking structure. Early completion of these reforms, in a proportionate way, will help us to contribute fully to the UK’s ongoing economic recovery."