More than one in 20 speeding offences detected by police in the Thames Valley were cancelled last year, figures reveal.

The RAC Foundation said the hundreds of thousands of fines cancelled each year across England and Wales are evidence that the system for catching and prosecuting speeding motorists is not working.

The charity's analysis of Home Office data shows that Thames Valley Police recorded 100,622 speeding offences in 2020-21.

Of these, 36,364 (36%) were dealt with by fixed penalty notices and 52,102 (52%) by speeding awareness courses, while 3,715 (4%) resulted in someone being taken to court.

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A further 5,954 (6%) were dismissed – up from 5% the year before.

Among the reasons why offences could be cancelled are faulty or incorrectly calibrated speed cameras, a lack of resources to bring cases to court, or cloned vehicles carrying a false number plate, according to the RAC Foundation.

Across England and Wales, 17% of all speeding offences were cancelled last year – an increase from 13% in 2019-20.

However, rates varied from 39% in Greater Manchester and Warwickshire, to just 2% in North Wales and Wiltshire – though the RAC Foundation cautioned that Wiltshire has no fixed speed cameras.

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Steve Gooding, director of the RAC Foundation, said it is important that the systems of detection and prosecution for speeding are robust.

But he added: "The hundreds of thousands of ‘cancelled’ offences each year indicate they are not.

"At the very least it is an administrative burden the police could do without.

“We urge the Home Office to start collecting data from police forces about these cancelled offences so we can understand where the problem lies.”

Dr Adam Snow, a lecturer at the Law School of Liverpool John Moores University, who worked on the report, said police forces and local authorities are seeing number plate cloning as a growing problem.

He added: "With the increasing reliance on camera enforcement for clean air zones and moving traffic violations there is some evidence to suggest more motorists are seeing this as an acceptable response even though it is fraud.”

The 2.4 million speeding cases detected nationally in 2020-21 – a period which included travel restrictions imposed to combat Covid-19 – was down 6% on the previous year.

The number of speeding offences also fell in the Thames Valley, down 19% from 124,512 in 2019-20, making it the lowest number since comparable records began in 2012-13.

The RAC Foundation said large disparities in the number of offences recorded by different police forces could be caused by the length and type of the road network, traffic volume, different policies by police and crime commissioners, and the availability of detection technology.

A Home Office spokeswoman said: “How the police deal with speeding offences is an operational matter and will be enforced at the discretion of the individual police force.

“Motorists must obey the speed limit, which is there to protect and benefit all road users.

"Forces may take a different approach to speed enforcement depending on local issues, such as targeting dangerous roads to reduce harm or cracking down on high-risk offenders.”