Police are failing to record thousands of reported crimes including rape and violence, a watchdog has warned.

Inspectors said the shortcomings mean victims are potentially being failed.

Her Majesty’s Inspectorate of Constabulary and Fire & Rescue Services (HMICFRS) rated  two forces – Thames Valley and North Yorkshire – as “inadequate” for crime recording.

The assessment of Thames Valley found that nearly one in five offences (19.6%) are not being properly recorded, which equates to approximately 35,200 crimes a year.

HMICFRS said reported crimes that go unrecorded by the force include sexual offences, domestic abuse and rape.

Inspector of Constabulary Zoe Billingham said: “I am disappointed with the quality of crime recording in Thames Valley.

“Although the force has implemented the recommendations from our previous crime recording inspection in 2014, we found that almost 1 in 5 crimes in Thames Valley are not being recorded properly – that equates to approximately 35,200 crimes a year.”

She said she was satisfied the force works very hard to ensure victims of crime are safeguarded.

Ms Billingham added: “It now needs to ensure that it records crimes at the earliest opportunity, and that there is proper supervision of crime-recording decisions.”

The report on North Yorkshire estimated that the force fails to record 9,200 reported crimes a year, including sexual offences, domestic abuse and rape.

Inspector of Constabulary Matt Parr said: “While our inspection shows that North Yorkshire Police has implemented most of the recommendations from our 2014 report, we still found of plenty room for improvement.

“As it stands today, we estimate almost 1 in 5 crimes in North Yorkshire are not properly recorded. This is simply inexcusable.

“The force has robust processes in place to ensure the safeguarding of victims of these crimes, but too many offences continue to go unrecorded and therefore not investigated properly.

“The force is potentially depriving victims of the services and justice to which they are entitled.”

Thames Valley Police said it accepted the findings and will be addressing the concerns raised.

John Campbell, the force’s Deputy Chief Constable, said: “This reports makes for unwelcome reading especially for a force that performs so well when measured in terms of our effectiveness, efficiency and legitimacy.”

He added: “The matters subject to review were recorded as ‘incidents’ rather than crimes, but there is no suggestion that we failed to respond appropriately to the calls or to deal with the matters in hand.

“I am pleased that HMICFRS confirmed that they found no issues of unethical behaviour and I can assure the communities of Thames Valley that every day, every officer is working hard to keep you safe from harm and to protect victims of crime.”

North Yorkshire Police Deputy Chief Constable Lisa Winward acknowledged the force needs to do “much better”.

She said: “Based on its inspection last year, HMICFRS found that although our officers and staff are focused on the needs of victims, our administration is letting us down, and we are not recording all crimes as we should.

“That must change, and we have already started to make improvements.

“It’s important to remember that every call we answer is logged; nothing is ignored.

“In every case where there was a vulnerable victim, we sent an officer and provided the service.”

The findings are the latest from a series of rolling inspections looking at the crime data “integrity” of every police force in England and Wales.

Inspectors launched the programme in November 2015 after finding the national average of under-recording of crimes stood at an “inexcusably poor” 19%.