The report, handed over to Interim Interior Minister Hamid Nawaz, an executive summary of which was released by the British High Commission, also concluded that a lone attacker fired shots at Bhutto and then detonated explosives at a rally in Rawalpindi on December 27.

"The only tenable cause for the rapidly fatal head injury in this case is that it occurred as the result of impact due to the effects of the bomb-blast," UK Home Office pathologist, Dr Nathaniel Cary was quoted in the report as saying.

"In essence, all the evidence indicates that one suspect has fired the shots before detonating an improvised explosive device. At the time of the attack this person was standing close to the rear of Ms Bhutto's vehicle," the British detectives concluded.

"The blast caused a violent collision between her head and the escape hatch area of the vehicle, causing a severe and fatal head injury," said the report, signed by Detective Superintendent John MacBrayne.