A nationwide child porn ring was smashed after a paedophile accidently left his mobile phone on a bus.

The chance discovery uncovered a paedophile ring involving more than 70 suspects across the country.

The handset was found on a local bus service in Newcastle by a passenger and was handed to the driver, who checked the phone in an attempt to identify its owner.

But he was horrified to find a series of images saved on its memory and immediately handed it to police.

They found that Michael Fraser had topped-up the mobile’s credit at the Tesco supermarket in the Newcastle suburb of Jesmond, and searched his home where they found a further 14 mobile phones - six of which were filled with child porn.

A forensic analysis of the handset revealed that 50-year-old Fraser was a member of a web of paedophiles stretching across the UK, who had been exchanging pictures and videos of youngsters.

After learning the extent of the network, detectives launched an operation - codenamed Cammell - which led to more than 70 suspects being identified, many of them were known paedophiles with a history of dealing in child pornography.

Dozens of investigations have been launched in police forces up and down the country as a result of the work done by detectives in Northumbria.

And wheelchair-bound Fraser, who now lives in Seaham, County Durham, has become the last of five perverts to be sentenced for their part in the ring at Newcastle Crown Court.

The court heard how he was traced after leaving his Sony Ericsson W580i on the number 100 bus travelling from the Metrocentre to Newcastle in February 2009.

Paul Simpson, prosecuting, said: “A mobile phone was found on a bus in Newcastle.

“It was found by a member of the public and handed to the driver, who looked at it, and it was apparent there were indecent images of children stored on its memory.

“That started a police investigation and the phone was traced to the defendant because it had been topped-up at Tesco in Jesmond, using a Tesco Clubcard, which was traced to him.”

Officers raided Fraser’s then-address, on Clayton Road, Jesmond, which led to the true scale of the ring being discovered.

Mr Simpson said: “The police went to his property and he had two phones in his possession.

“He threw one of them onto the bed and the police also found a number of other phones, 12 to be precise, inside the premises.

“There were 14 in total inside that room and six of those had these images stored on them.

“What was apparent was that the one thrown on the bed had had 11 separate Sim cards used in it.”

Between all the phones found to contain child porn, Fraser was found to be in possession of 371 images, more than 80 of which were later categorised as level four, the second most revolting.

An analysis of messages received by the handsets led detectives to others, who in turn had their phones seized and interrogated.

The investigation grew rapidly, as more and more suspects were identified by the pictures and videos they had been sending between each other, often in exchange for mobile phone credit.

Fraser admitted nine counts of being in possession of indecent images of children and five of making indecent images of children, which related to pictures being sent between different mobiles found in his room.

He also pleaded guilty to two counts of the possession of extreme pornography.

He also asked for offences relating to a further 89 child porn pictures to be taken into consideration when he was sentenced.

Brian Hegarty, defending, said: “The defendant accepts that he has an unhealthy interest in children, which is of many years standing.”

Judge John Evans told Fraser the offences he committed, despite not being convicted of distributing images, could have attracted a prison sentence.

But after the Probation Service said he was eligible for sex offenders’ treatment, he decided not to lock him up.

Instead, Fraser was give a three-year community order, ordered to sign the sex offenders’ register and given a Sex Offenders’ Prevention Order, which means he must not use computers or phones for sending or receiving images and is prevented from taking pictures in public of anyone under 16.