Police have asked the Home Office for at least £6m towards the cost of investigating the UK's biggest cash robbery in Kent.

The inquiry into the £53m depot raid in Tonbridge has led to 11 people being charged, two further arrests and an extradition request.

Chief Constable Mike Fuller said: "Our own view is this is unique as far as robberies and armed robberies go.

"We hope the Home Office will support us in paying some of the costs."

The police chief said an answer was expected from Home Secretary John Reid in the next three weeks.

Mr Fuller said the force had so far recovered £21m of the cash that was stolen in February and detectives were still pursuing leads in relation to the rest of the money.

He said: "It's certainly reputed to be one of the biggest cash robberies in the world.

"It's something that we couldn't have foreseen and we don't often ask the Home Office for money for investigations because obviously we are funded for that."

Mr Fuller said the £6m would go towards expenditure so far and also towards future spending on the trials and preparations for the court cases.

On Friday, a Home Office spokeswoman said: "We have received a request from Kent Police which is currently being considered."

This month, two men were arrested on suspicion of conspiracy to commit robbery in the Securitas raid in Tonbridge and bailed until 8 February.

Four women and seven men charged in connection with the robbery have been remanded to appear at the Old Bailey in London on 15 December.

Police are also seeking the extradition of another man, Lee Murray, a 26-year-old martial arts expert from Sidcup, south London, who was arrested in Morocco on 25 June.

Mr Murray is in custody pending extradition proceedings.