The Crown Prosecution Service is failing to prosecute honour crimes for fear of causing “unrest” in Asian communities, a Scotland Yard whistleblower has alleged.

Det Sgt Pal Singh disclosed that “apathy” by prosecutors led to the collapse of what could have been the first conviction for forced marriage in England.

He said that the CPS dropped the case despite pleas from the police that “a forced marriage trial would send a strong message to the community”.

Det Sgt Singh has been commended three times by the force for his work in the area over the past year.

It is extremely unusual for a serving police officer to publicly attack the CPS, which is facing an unprecedented wave of criticism over its prosecutions in child sex abuse cases, rape inquiries and a string of failed prosecutions against journalists.