LONDON (Reuters) - HSBC, Europe's biggest bank, said its UK mortgage lending jumped to four times its normal rate in the past month after it launched an offer to grab a bigger slice of the market, which it will now extend.

HSBC said since launching its "rate matcher" offer on April 14 it had averaged over 100 million pounds in mortgage sales daily, four times its normal volume.

That indicates the bank's gross lending was over 2.5 billion pounds in the last month, and may have given it a market share of over 12 percent.

HSBC has previously had an underweight position in UK mortgages, with just 3.6 percent of the market. It launched its offer to exploit rivals' weakness in the global credit squeeze, which has seen most banks scale back on lending, withdraw offers and tighten criteria.

HSBC plans to extend the offer for a further six weeks to June 29.

It said credit quality had remained strong and the average mortgage represented only 56 percent of the value of the property it was secured against.