National Australia Bank may pump up to 387 million pounds ($A664.79 million) more into its British arm Clydesdale amid increasing pressures from UK regulators to aid local units .

NAB won approval to provide the fresh capital for Clydesdale at a general meeting of the subsidiary held in London July 1.

UK's Financial Services Authority is among regulators urging banks to hold better quality capital amid renewed concern over the stability of Europe's financial system.

While Clydesdale has surpassed most of its British rivals, it has become a big drain on the NAB's capital resources in the past year as bad loan losses have soared.

Clydesdale's profit of 4 million pounds in the six months to the end of March, was far behind the 30 million a year earlier. Bad debts climbed 12 per cent to 188 million pounds.

Since December 2008 the paid-up capital committed to the British arm has quadrupled from 254 million (A$436.2 million).

Clydesdale will have a capital base of more than 1.04 billion (A$1.77 billion) after the latest injection from NAB.

According to a NAB spokesperson, Clydesdale had received approval from its board to issue up to 387 million (A$664.6 million) of fresh Tier 1 capital.

"This is a business-as-usual activity which is consistent with similar moves taken by other global banks to continue to strengthen their capital positions."

"The capital issue has not yet been fully executed."