Almost three-quarters of police forces have forked out more than £22m on body-worn cameras, but are failing to properly monitor how the videos are used in court, according to a report released today.

Proponents of the technology argue it will improve transparency in frontline policing, stop police and the public from behaving badly and speed up court proceedings by encouraging earlier guilty pleas.

But civil liberties group Big Brother Watch – which compiled its report based on Freedom of Information requests to all 45 UK forces – said there wasn't enough evidence that it had a positive impact on policing.

Some 42 forces responded to Big Brother Watch's FOI, and of these, 32 (71 per cent) said they used body cameras, with 47,922 purchased so far. A further four forces said they were either trialling them or planning to roll them out for the first time.

The total spend revealed by the FoI is £22,703,235, but the figure is likely to be higher as some forces refused to release their figures.

This includes Greater Manchester Police, which has 3,148 cameras in use – the second highest figure across the group. It said the information was commercially sensitive, but reports from 2016, when the project was launched, put the figure at £2m.

The biggest spender was London Met, which spent £15.5m on 22,000 cameras, and yesterday revealed it was kitting out all of its armed response units with body-worn video.

The data also shows that Reveal is the most popular manufacturer among forces, selling its kit to 19 of them. But Axon's lucrative contracts with the London Met and Greater Manchester Police mean it provides more units overall, a total of 26,935, despite only supplying four forces.

The data is stored on internal force servers, the cloud (London Met is planning to move to a UK-based Azure solution) and burnt onto disc. In line with police rules, the forces said the data was stored for no more than 31 days unless required for evidence.

But is the evidence used in court?

However, the forces failed to provide responses to FoI questions about how the data generated by body-worn cameras had been used.

Big Brother Watch asked how many court cases had successfully and unsuccessfully used footage from body-worn vids, but none offered up the information.

Seven forces said the information wasn't held, one said it wasn't recorded at all, while others said the data wasn't collated or held in an accessible format. The rest refused based on the cost and time it would take to gather the information.

For those following criminal justice system and digital policing reforms, the lack of good quality, well-collated data will not be a surprise.

Big Brother Watch said it was "not good enough" to say video evidence was having a positive impact when there wasn't data to back that up, and called on the police to store data in a readable and accessible format, and for it to be published as part of an annual review of the technology.

Whilst we appreciate that systems may not have been originally established to record the use of footage in an easily readable format, the failure to seek to build systems to record the use of footage in a prosecution or in relation to an early guilty plea is of profound concern. With no access to the facts and figures relating to the outcome or how footage from body-worn cameras is used it is impossible to assess the claims of their value. If the police and CPS are insistent that the technology will improve sentencing and improve guilty pleas they need to provide data to show the assertion to be accurate.

However, Stephen Goodier, former staff officer to national body-cam lead Chief Constable Marsh, said: "Only a very small amount of body-worn video evidence will be used to support the prosecution case. Otherwise, using [the] tech adds to the bigger, richer picture, making the police more transparent and accountable.

"At the moment, data collection across the criminal justice system is not that joined up and a lot of the data processing is manual. If proposed plans to streamline these systems are a success – and we move towards a cloud-based system – it will be easier to identify and track where evidence is used."

Big Brother Watch also urged cops not to start using body-worn cams in other ways – such as gathering more up-to-date images of known crims through stop and search – which it said was "far removed" from the purported purpose of improving relations between the police and public. ®