A fifth of crimes — amounting to tens of thousands of offences — may be going unrecorded by police, a damning report by the force’s watchdog has found.

An inspection of 13 forces by HM Inspectorate of Constabulary (HMIC) found that out of a sample of 3,102 incidents, 2,551 crimes should have been recorded but 523 were not, including sexual offences, violent crimes, robbery and burglary.

Fourteen rapes were among the offences not recorded, including an allegation made by a 13-year-old autistic boy which was written off as “sexual experimentation.”