The Spanish bank, which owns Alliance & Leicester and Abbey for Intermediaries in the UK, made a group profit of €2.2bn (£1.9bn), up 6% from Q1 last year.
Santander UK estimates it has a gross mortgage market share of 20%, meaning the bank writes one in five UK mortgages.
This represents a 5% increase from the 15% gross market share the bank had this time last year.
Net lending for Q1 was £1.4bn, while gross mortgage lending was £5.7bn.
The bank’s mortgage book is running a three-month arrears rate of 1.41%, compared to the Council of Mortgage Lenders industry average of 2.38% for Q4 2009.
Out of its total book 0.07% of properties have been repossessed, against the CML average of 0.14%.
The average LTV of new business was 61% for Q1, with the average LTV for existing business at 52% LTV.
António Horta-Osorio, chief executive at Santander UK plc, says:”Our first quarter performance shows that our business model continues to deliver improved
performance, increased market share and sustained profit growth.
“We are continuing to share the benefits of being the most efficient UK bank with our customers, offering better value for money products rewarding their loyalty through innovations like our Zero current account.
“The success of our rebranding is clearly demonstrated by further growth in mortgage lending and customer deposits.
“We have also shown the strength of our small and medium-sized enterprise proposition where we increased lending by over 18%, showing our commitment to this essential sector of the UK economy.”