Four Kenyan police officers are to be charged with the murder of a young British aristocrat who died in their custody six years ago.

Defying expectations, a Kenyan inquest ruled on Thursday that Alexander Monson died as a result of “blunt force trauma that could only have been caused when the deceased was in the custody of the police.”

The ruling represented a stunning breakthrough for Nicholas Monson, the 12th Baron Monson, whose long campaign for justice for his son had been thwarted at so many turns.

The police officers who held Mr Monson after he was detained May, 2012 on suspicion of possessing a joint of cannabis long claimed he had died of a drugs overdose.

But the magistrate entirely rejected their claims and within minutes of his ruling Kenya’s new director of public prosecutions had ordered the arrest of the four policemen.

Kenya, as many Kenyans would attest, has a reputation for official impunity, particularly its notoriously brutal police force.