LONDON: A cage fighter began his 18 years jail sentence Tuesday after admitting involvement in the country's biggest ever cash robbery, a 53 million pound raid at a security depot.

Paul Allen, 31, who fled to Morocco and lived a life of gambling and drug-taking after the raid, pleaded guilty last week to three charges of conspiracy to kidnap, conspiracy to rob and conspiracy to possess firearms.

Allen was arrested in the Rabat area in June 2006 and extradited in January last year.

Five men have already been convicted over the 2006 robbery in Tonbridge from which police have recovered just 21 million pounds.

During the raid, the depot manager and his family were kidnapped and 14 members of staff were tied up at gunpoint.

Allen admitted the crimes on the basis that he did not enter the depot and did not help to kidnap the manager and his family.

He pleaded guilty just before he was due to face a retrial at Woolwich Crown Court in southeast London.

In cage fighting, muscle-bound competitors with backgrounds in different styles, such as karate, boxing and wrestling, take each other on inside a cage, with few rules.

The Ultimate Fighting Championship is the highest-profile mixed martial arts contest.

US film director Darren Aronofsky is reportedly set to make a Hollywood movie about the robbery.