LONDON (Reuters) - Britain froze $100 million linked to alleged swindler Allen Stanford within five hours of a request from the United States Department of Justice, anti-graft officials said yesterday.

The once high-flying billionaire and sports promoter, who faces life in prison if convicted of all 21 criminal charges against him in relation to a $7 billion Ponzi scheme, last week pleaded not guilty.

Britain's Serious Fraud Office (SFO) said yesterday that it had obtained a restraining order on assets believed to be held by financial institutions in London on April 7.

"These funds were allegedly acquired in connection with a suspected $7 billion investment fraud scheme operated by Stanford," the SFO said in a statement.

The SFO said it felt able to release details of action taken by British authorities because Stanford had now been taken into FBI custody as part of a criminal investigation.

SFO Director Richard Alderman said he was determined such cross-border support for US authorities became routine.

"I am delighted that the SFO has been able to secure a freezing order of this magnitude and within five hours of it being requested," Alderman said.

Britain's Crown Prosecution Service and London police also assisted the US authorities with their inquiries, the SFO said.

The watchdog said it had recently reviewed procedures related to the freezing of assets believed to be the proceeds of crime and that it was earmarking dedicated resources.

"The organisation aims to increase the volume of assets restrained, confiscated, recovered and - in the future - forfeited," the SFO said. "It also aims to increase the potential for compensation payments."

Shockwaves from the latest scandal involving a US financier have been felt across the globe, not least in the Caribbean and South America where investors besieged Stanford's banks to redeem funds when fraud charges emerged in February.

In Britain the normally tranquil world of cricket was badly shaken by the saga given Stanford's multi-million dollar sponsorships and a visibly glitzy influence that drew criticism from some quarters of the game.

Fleeced investors cheered and applauded on Monday when disgraced financier and former Nasdaq chairman Bernard Madoff was sentenced to 150 years in prison for what was Wall Street's biggest investment fraud.