A postman caught masturbating in a supermarket car park for the second time was "sexually frustrated" as he watched young women walking into the store.

Grenville Porter was spotted performing the sex act by a father while he was helping his two young children out of the car at Tesco on Sealand Road, Chester.

The 62-year-old, who works for the Royal Mail, was parked next to the family when he became "sexually frustrated" at around 4pm on July 1 this year.

It is the second time that the postman, from Meynell Place, Blacon, has been convicted of masturbating in supermarket car parks - in 2009 he performed the sex act outside a Morrisons supermarket.

But Porter denied he was committing the lewd act for attention, telling Chester magistrates he had been "sexually frustrated" at the time and knew it "was wrong".

Porter, who represented himself during the hearing at Chester Magistrates Court today (Monday), said: "According to the probation officer, she thinks I do it to get attention, I do not.

"On the occasion I did it because I was sexually frustrated."

The court heard how a father was helping his two young children out of the car when he spotted the driver of the car next to him behaving oddly.

"Initially the witness thought he might be scratching himself," said Caroline Viviani, who said Porter became aware that he was being watched and his movements became more vigorous.

"He appeared to turn towards a young female who was crossing the car park," she added.

The witness, who had moved his family away from the car, informed a police officer at the time of the incident, which happened when several shoppers were in the car park.

Porter was sentenced to a community order and supervision requirement for three years after pleading guilty to the act of outraging public decency.

He was made subject to a curfew for 28 days, between 7pm-6am, but Chester magistrates removed it for two days so that he could attend his son's wedding, saying they would add the days on to the end.

Porter was also ordered to take part in a sex offender's programme and ordered to pay £85 court costs and a victim surcharge of £25.