A sharp eyed car passenger helped to bring to justice a 41 year old man sexually exploiting a girl of 13, a judge heard on Friday.

Charles Rutherford had parked his van at a layby at Pope Hill, Johnston, and followed the girl into the ladies' toilets.

But he had been seen by Benjamin Hawthorn, who had been a passenger in a car parked at the same layby, and he went into the gents' to find it empty of people.

Assuming that the man was still in the ladies' Mr Hawthorn telephoned the police and two female officers entered the toilets.

Patrick Griffiths, prosecuting, said one went into the ladies' and found one cubicle locked. She banged on the door and shouted "police" and after a short while Rutherford opened the door as he and the girl continued to adjust their lower clothing.

The girl was taken into police protection and driven home. Eventually, she confessed that she and Rutherford had been having a relationship.

Rutherford was arrested and he and the girl's mobiles were examined. Police found more than 1,500 text messages from him to her and 950 in the other direction.

The messages, said Mr Griffiths, made it clear what had been happening.

Rutherford, from Llanelli, admitted two offences of engaging in sexual activity with a child, one involving sexual intercourse.

Ian Wright, the barrister representing Rutherford, said he lived an isolated life and had thought that he was in a loving relationship, despite the obvious difference between their ages.

Judge Christopher Vosper had, he said, a "stark" choice between jailing Rutherford or making him the subject of a community order that would include treatment and education.

Judge Vosper said the offending was too serious and jailed Rutherford for two years and eight months.

It was clear, he added, that some sexual touching had been going on in the toilets at Pope Hill.

Rutherford was ordered to register with the police as a sex offender and, in due course, will be banned from working with children or vulnerable people.