Fines for drivers using drugs, alcohol, phones, and not wearing seatbelts have slumped, while speeding numbers caught by cameras rise

Inspectors found that one force was only able to process nine blood samples per month due to limited capacity at the lab and tight budgets.

A report on roads policing in seven forces in England and Wales said: "The inescapable conclusion is that offenders who are suspected of driving while under the influence of drugs are being tolerated and allowed to present a continuing threat to communities.

"We don't believe that this is acceptable."

Her Majesty's Inspectorate of Constabulary and Fire and Rescue Services (HMICFRS) also revealed that the number of alcohol breathalyser tests slumped by a quarter between 2015 and 2018 - from 425,325 to 320,988 - at a time when the number of deaths caused by drink drivers rose.

Other enforcement measures also dropped, with the number of fines for not wearing a seatbelt falling 75% from around 86,300 in 2013 to about 21,600 in 2018.

During the same period the proportion of car occupants killed in crashes who were found not to have been wearing a seatbelt went up from 20% to 26%.

The number of fines given to drivers using their phone also dropped from around 162,400 in 2011 to 38,600 in 2017, although the number of phone-related crashes stayed level.

In contrast the number of speeding tickets, mostly where drivers were caught by a camera, rose by 41% between 2011 and 2018 to 2,105,409.

There were suspicions that the cameras were being used to generate revenue, inspectors found. While police forces do not receive money from traffic fines, they are able to claim back administration costs.

The report said that in one force "we were told that the reason enforcement took place at certain locations was that they were 'good hunting grounds', rather than because they had a history of collisions".

The watchdog called for roads policing to be treated as seriously as efforts to counter terrorism and organised crime, in view of the number of deaths on the roads, the cost of closing major highways and the links with other areas of law enforcement.

Between 2016 and 2018, 4,872 people died and 69,580 were seriously injured as a result of road traffic collisions in England and Wales.

The number of road deaths declined steadily from 1979 to 2013, when figures levelled off. Between 2015 and 2018, an average of 1,610 people lost their lives each year.

The financial cost of all road accidents is estimated at £36 billion per year, and in 2011 the estimated cost of motorway closures was £1 billion, the report said.

HMICFRS inspectors raised concerns that the importance of roads policing was not being appreciated, with less than half of forces - 19 out of 43 - listing it as a priority.

In one area, where more than 100 people had been killed in road accidents in a four-year period, the police and crime commissioner told inspectors they were "not aware of anything that made us worry about it".

Annual spending on roads policing dropped by around 34%, or £120 million, between 2012/13 and 2019/2020.

Staffing shortages meant one force had one roads officer responsible for an entire county on some shifts, while in another patrols stopped at 2am, the report found.

In total seven forces were inspected. Both the Metropolitan Police and West Midlands Police were praised as "notable exceptions" for their work in roads policing.