A reporter who answered a graffiti advert on a train toilet door asking for young girls for sex uncovered a paedophile ring.

Ruth Lumley, who works for The Argus, alerted police who launched a ten-month investigation spanning several counties which found that eight seven to 13-year-old girls had been subjected to "horrific" abuse.

Four paedophiles - including two men from Sussex - are now facing long jail sentences after pleading guilty to a string of sex offences.

The case involved graffiti advertisements on Sussex trains touting for "girls aged eight to 13 wanted for sex".

On one occasion a young girl was offered for abuse in return for cash.

It was one of the sickest cases police have dealt with and officers who had to view obscene pictures and videos have been offered counselling.

The last of the men yesterday pleaded guilty at Hove Crown Court and sentencing for all four was adjourned.

Ringleader Trevor Haddock, who threatened to kill one of his child victims if she told anyone, could face a life sentence.

The 54-year-old from Worcester was charged with 59 counts but the prosecution accepted guilty pleas to 13, including rape, sexual assault, making and taking indecent videos and photographs.

Ian Jones, 42, of Rowlands Road, Worthing, admitted six offences including graffiti, attempting to incite a child to engage in sex and conspiracy to commit sexual assault on a child.

John Farmer, 67, of Peelings Lane, Westham, Eastbourne, pleaded guilty to facilitating or arranging the commission of a child sex offence.

The fourth defendant, Derek Moody, 44, from Newcastle, admitted incitement to the rape of a nine-year-old girl.

The gang was brought to justice with the help of Miss Lumley, 26, who was travelling from Chichester to Brighton when she noticed the graffiti advert in a toilet on her train.

She took down the mobile number but there was no answer when she tried it. Unknown to her, British Transport Police (BTP) were already investigating and had found 22 such daubings in toilets on trains, in stations and in toilets in two pubs, one at Brighton Station's Britannia Bar.

Miss Lumley later that day received a text message asking how old she was. She pretended to be a girl of 11 and during that evening was bombarded with sexually suggestive and lewd messages. Miss Lumley did not reply but contacted police.

The mobile number she gave them turned out to be from a pay-as-you-go phone and was virtually impossible to trace.

A BTP officer then sent a text. The officer pretended to be a 12-year-old girl called Amy and arranged to meet a man outside the Burger King restaurant in Madeira Drive, Brighton.

Police were lying in wait and they arrested Ian Jones, a man convicted of attempted rape in Burgess Hill in 1985.

They searched his flat in Worthing and checked his phone records. They discovered calls to John Farmer in Westham.

Farmer was arrested when child abuse pictures were found on his phone. Two pictures found on Jones's phone were taken in his flat and included an image of a third man who Sussex Police later identified as Trevor Haddock.

They raided Haddock's home. Examination of his phone records led to the uncovering of a plan by Haddock to take a young girl to Newcastle so she could be abused by the fourth defendant Derek Moody in exchange for cash.

Police stepped in before the deal was completed.