A "champion" foster-carer from Ystradgynlais has today been exposed as a life-long paedophile.

Christopher Purnell, of Minyrhos, was downloading indecent images of children until days before he was arrested - more than 30 years after he began offending.

The 62-year-old, once the chairman of his local county-wide foster carers association, had also set up a help line for children in distress.

But a jury at Swansea Crown Court heard he was one of the perverts causing the distress.

Purnell was convicted of 22 offences of indecency with a child, indecent assault, sexual activity with a child and making indecent photographs.

He was jailed for seven-and-a-half years and ordered to register with the police as a sex offender for life.

Purnell had denied the charges and called his accusers liars.

The jury heard that police computer experts were able to discover that Purnell had trawled the internet using terms like "teenage nudist, "boys in licra tights" and "boys in boxers."

Purnell told the jury he had been researching material for a book he was writing on naturism. But it was never published.

One victim told how Purnell had taken photographs of him naked when he was a boy, telling him he had a customer who paid according to how dirty they were.

The man said he agreed to pose because he thought the money might lead to a better life.

"He kept on and on about a man willing to pay thousands of pounds for real photographs of my genitals. Even afterwards he asked me for more and more, saying the first ones had not been valuable enough," added the witness.

He said Purnell threatened that he could use his power to have him put into a remand home if he did not co-operate.

"He told me that the best oral sex I would ever get would be from a man because a man knew what to do. I have never forgotten that. I was really shocked. He offered to try it with me."

Purnell boasted to one boy about his importance in fostering, and how he liaised with the local authority's social services department.

He advised the boy to contact him if "I ever had any problems with my private parts."

Purnell also got a teenage boy drunk. The boy woke up the following morning without any pyjamas on and "feeling really bad."

Detective Constable Simon Davies said three of Purnell's computers turned out to be "of interest." One showed that he had downloaded child pornography at 3.31am on January 28, 2012, only a few days before he was arrested - and while his innocent wife Susan had been asleep in bed.

John Hipkin, prosecuting, said Purnell's sex offending dated back to 1982, when he indecently assaulted a boy, an offence for which he was convicted. He was also found guilty of making indecent photographs of a child in 2012, as well as 20 crimes in between.

After the jury returned guilty verdicts, one of Purnell's victims said, "No-one could say anything against him in those days, he was a champion of fostering. And no-one was going to believe what I had to say.

"He was always going on about he was chairman of this, chairman of that.

"At the age he assaulted me it is very worrying and I accepted what I was told.

"Now, Purnell is where he belongs, in jail," he added.