The police investigation into the deaths of Holly Wells and Jessica Chapman could cost as much as �10m.

A report for Cambridgeshire's Police Authority says the total cost of the inquiry is already more than �5m and could double.

The authority is to ask the Home Office for extra money to cover the increased costs of the operation.

Cambridgeshire officers gave up their holidays and put in hundreds of hours of extra time when the hunt for the missing girls turned into a murder inquiry.

Holly and Jessica vanished from Soham on 4 August

Recorded costs so far total �320,000, but hundreds of officers from 21 other forces were also drafted in to help and have yet to submit their bills.

Although the total cost could run to �10m, the authority insists the final bill is still being totted up.

A spokeswoman said: "The authority would like to make it clear that at this stage these figures are only an early pre-estimate and that full costs are still being calculated.

"The constabulary is still at the stage where it is waiting for and adding up bills in relation to this inquiry."

The chairman of the Cambridgeshire Police Authority John Reynolds said: "Everyone wants to make sure that this particular case is completely resolved and funding is not an issue.

"We are hopeful that (the Home Office) will receive our request sympathetically.

"It would cause significant embarrassment if we did not get a sympathetic ear.

"But until we have a proper assessment, we will be in a difficult position to judge what happens one way or another."

Murder charge

Operation Fincham was Britain's largest investigation of this type, involving 426 officers from 21 forces.

Former Soham village caretaker Ian Huntley, 28, has been charged with the murder of the two 10-year-old girls and with conspiring to pervert the course of justice.

His girlfriend 25-year-old Maxine Carr, a learning support assistant at the girls' school, is charged with attempting to pervert the course of justice.

The bodies of the two best friends were found on 17 August in a copse near the American air force base at RAF Lakenheath in Suffolk.