Specialist police units that analyse phones and computers in suspected child abuse cases are grappling with lengthy backlogs of more than a year, according to new data.

A freedom of information (FOI) request sent to every UK police force by BBC Radio 5 Live Investigates revealed more than 1,800 cases were still waiting to be processed.

According to the FOI data, the longest delay recorded was for Wiltshire Police where a case was still awaiting forensic examination after one year, nine months and 19 days.

More than half of UK police forces reported delays of at least three months where cases were "waiting to be allocated" to a member of staff in the high-tech crime unit for analysis.

Five forces had devices which had not been examined after more than a year.

High-tech crime units are tasked with retrieving evidence from electronic devices in cases of suspected child sexual exploitation, with the information often key to securing convictions against paedophiles who use the internet to groom youngsters and go on to abuse their victims.

The BBC's results showed that, among the UK's regions, Northern Ireland had the oldest outstanding unallocated case dating back 18 months.

In Wales, the oldest case, being dealt with by North Wales Police, dated back seven months.

Two police forces in Wales; Dyfed Powys and South Wales were able to allocate cases within two weeks, while Gwent Police did not respond.

Police Scotland's longest delay was 10 months.

One mother who contacted police over suspicions her daughter had been exposed to grooming attempts via chat rooms and webcams from the age of 13, said she was "shocked" to be told there would be a six-month delay in examining computer data.

Speaking anonymously, she told the BBC: "They wanted the laptop and her phone so we handed them over, and they did say 'we don't know how long it will take' because they had quite a backlog going back to January and this was July.

"I was shocked. My daughter was probably just one of many people they were talking to. These are children that need protecting."

She added that their case was accelerated by the police but only after her daughter took an overdose.

In July this year a separate report by Her Majesty's Inspectorate of Constabulary (HMCI) which examined 124 cases at random in six police forces found delays of 12 months were "not uncommon".

It concluded that "these delays increase the risk to children".

One force, Lincolnshire Police, which has a backlog of 10 months, has expressed "regret" that the cases it deals with have to be prioritised, meaning some cases take longer.

Detective Superintendent Guy Collins, of Lincolnshire Police, told BBC Radio 5 Live Investigates: "We have to prioritise, that's the sad reality of life. We can't do everything straightaway."

He added that incidents involving high-risk suspects were always dealt with more swiftly than others but admitted this meant other cases would be pushed further back in the queue.

"It is a matter of absolute regret that we can't do all of those as quickly as we'd like to but we do work very hard to protect children," he said.

Lincolnshire Police and several other forces are now allocating additional resources to their high-tech crime units.

The Minister for Preventing Abuse and Exploitation Karen Bradley told the BBC: "We are committed to ensuring police have the resources they need and we have prioritised child sexual abuse as a national threat.

She added: "We have allocated additional funding of £10 million to the National Crime Agency (NCA) to track down offenders and protect children and launched the Child Abuse Image Database which will reduce the time taken to identify illegal images."