A man who raped two young girls and sexually abused another two over a 20 year-period was today jailed for 12 years.

John Robertson was finally brought to justice by a letter written to an agony aunt.

The note, which was written by one of John Robertson's rape victims and not sent, was found by a family member in 2002 who read the heartbreaking letter and police were called in.

The letter stated: "For the last seven years John Robertson has sexually abused me. I am ashamed and embarrassed. Can you help me?"

But it was nine years later before Robertson was charged with his vile crimes after other victims came forward.

Sentencing 45-year-old Robertson Judge Michael O'Grady QC: "You have been convicted of an appalling course of conduct . You spent years preying on children. You abused the complainers when they were aged between eight and 15.

"Two of them were raped on seven occasions... with some of your victims have blighted their young lives and with some you have ruined and haunted their adult lives."

At the High Court in Glasgow, Robertson, who shows guinea pigs, denied all the charges against him and claimed his victims now women were making up lies in order to claim compensation.

Judge Michael O'Grady QC told Robertson: "You have been found guilty of an appalling course of conduct, years of preying on vulnerable young women time and again.

"Your behaviour blighted their childhood and haunted their adult years."

The offences were committed between 1990 and 2002 at Mansefield Farm, Garshangan Road, Kilmacolm.

The victim, who wrote the letter is now 26 and she told advocate depute Jane Farquharson, prosecuting" "I can't remember how many times I was raped."

The woman added: "I thought that it kind of happened to everybody and once I realised it didn't I thought I should have said something sooner, but I didn't know how to stop it."

Another victim, who was sexually abused by Robertson said that she 'just froze" while he touched her inappropriately..

A further charge of rape was found not proven against Robertson.

Robertson has previous convictions for minor road traffic offences.

The court heard that Robertson maintains his innocence to all charges.