Gary Thomas was jailed for 18 months

A Mold Crown Court judge imposed the five-year restraining order - thought to be one of the first in the UK - against Gary Geoffrey Thomas, 37.

He also jailed the railway guard from Swadlincote, Derbyshire, for 18 months.

Thomas, who had claimed to be 20, made 1,700 calls to the mid Wales girl and admitted three counts of unlawful sex.

Judge Huw Daniel told Thomas, who also admitted five charges of possessing child porn off the internet: "I regard these offences as being aggravated by the fact that you are a predatory paedophile.

There is very little scope to operate a sentencing exercise that takes into account his paedophilia Judge Huw Daniel

"The sooner that you come to terms with that description the better it will be for everyone, especially young girls."

He said he had wanted to jail Thomas for 10 years but that the law dictated the maximum sentence he could impose was a two-year term. The judge had also had to take Thomas's guilty plea into account.

He urged the government to change the law, condemning the "idiocy" which limited the sentence of men like Thomas but meant men who had unlawful sex with girls just one year younger could be jailed for life.

"There is very little scope to operate a sentencing exercise that takes into account his undoubted paedophilia," he added.

'Deliberately targeted'

Prosecutor Steven Everett said that Thomas had met underage girls through internet chatrooms, then bombarded them with phone calls and text messages on their mobile telephones.

He said Thomas had deliberately targeted and groomed the 14-year-old from the Welshpool area of Powys - one of 15 girls he had contact with aged between 13 and 16 - before visiting her home and having sex with her.

Thomas had denied two further charges of having unlawful sex with the girl and abducting her, which were left on the file when the prosecution offered no evidence against him.

Speaking after the trial, Detective Sergeant Diane Davies told BBC Wales it had been a difficult investigation involving nine policing areas.

When asked about the restraining order - which bans Thomas from subscribing to, or using, the internet or any mobile telephone for the next five years - she conceded police could not stop him using the equipment.