Britain was left isolated at a meeting in Brussels on Tuesday after it failed to water down new European union rules that will cap bankers' bonuses, a measure that could threaten London's dominance as a global financial centre.

In a lively exchange in parliament with the leader of the opposition Labour party, Cameron struck a defiant note on Wednesday, using language that stoked speculation his government might be contemplating invoking its national interest to try to delay or amend the draft EU directive.

"There is an important issue here. There are some important British national interests," Cameron told parliament. "We are responsible for 40 percent of the EU's financial services ... (and) we want to make sure that international banks go on being headquartered here in the UK."

But his official spokesman later made it clear that Cameron's language did not signal any change in tactics on the issue and played down the idea that Britain might try to delay the legislation by arguing it threatens its national interest.

"The right thing to be doing is for there to be this process of discussion over the implementation of this directive," the spokesman told reporters, saying Britain would be seeking technical amendments in talks in the weeks ahead.

The issue is a tricky one for Cameron. On the one hand, he is under pressure to be seen to be protecting the City of London, a sector that former European Commissioner Peter Mandelson has likened to Britain's "golden goose", underlining its importance to the $2.5 trillion economy.

But bankers have become public hate figures since the 2008 financial crisis and are regularly castigated by voters and politicians, making it politically difficult for Cameron to style himself as their defender.

POLITICAL ATTACK

Ed Miliband, the leader of the Labour party, on Wednesday accused Cameron and his finance minister of being the only people who felt it was "a priority to fight for bigger bonuses for bankers", using a by now familiar line of attack that tries to cast Cameron, who hails from a privileged background, as someone who rules for the rich at the expense of the poor.

But Cameron, who regularly accuses Labour of having mismanaged the economy before he came to power in 2010, said bankers' bonuses were a quarter of what they were under Labour.

"I don't have to listen to the croupier in the casino when it all went bust," he shot back at Miliband.

Earlier on Wednesday, Bank of England official Andrew Bailey - who will be in charge of day-to-day regulation of British banks from April - also criticised the EU proposals, saying the rules would not make bankers take fewer risks.

Limiting variable bonuses would simply push up the fixed part of bankers' remuneration, making it harder to cut costs in a downturn or claw back pay in cases of malpractice, reducing the incentive for bankers to think long-term, he said.

"Losing those two incentive mechanisms before we get to a solution for the 'too big to fail' problem is something that concerns me," he told legislators reviewing British banking law.

However, both he and Bank of England Governor Mervyn King played down the longer-term significance of the bonus rules for Britain's position as a financial centre. A bigger threat was that banks were still too large and complex to shut down if they got into trouble, King said.