A plumber who used a household water tank to

dispose of a leak of his own was warned he faced jail today.

Roy Williams, 46, of East Grinstead, was convicted by a jury of attempted deception, making a false trades description and making a reckless statement when called out to fix a "fault" at a house which was being used for an undercover Trading Standards sting operation.

While he was in the loft of the house, Williams was secretly filmed urinating into a vase and tipping it into a water tank by trading standards officers hidden in a room just feet below him.

Williams, who gave his address as Allways Maintenance limited, of West Hoathly, East Grinstead, claimed he had been overcome by the effect of "bright lights and the sound of running water".

Williams, who said he had been in the plumbing trade for 11 years, claimed he suffered from a medical condition dating back to a piles operation when he was a child which left him needing to use the toilet regularly.

Guildford Crown Court heard that, after tipping his own urine into the household hot water tank, he dipped the vase into the house's cold water storage tank to rinse it out, forcing trading standards officers to pay almost £700 to have the system flushed out.

Williams thought he had been called out on a job to fix an overflow in the hot water tank.

Unknown to him, the house had been rigged up with hidden cameras concealed in everyday items including a cornflakes box, a rubber duck and a brown suitcase to film tradesmen carrying out the jobs to test their honesty.

On November 4, 2003, plumbing expert Colin Topp had set up a "fault" by displacing the jacket of the tank on to the arm of the ball cock causing an overflow.

Shortly after arriving in the loft, Williams sent his apprentice back to the van to fetch two valves which, the court heard, did not need to be used.

It was while his apprentice was away that Williams, who charged £96 an hour plus a call-out fee for his efforts, took advantage of the private moment to attend to his own waterworks.

Cross-examined on his indiscretion, Williams said he thought he was too desperate to bend down and use the ladder to get to the toilet below.

During lengthy cross-examination Williams twice had to leave the witness box to use the lavatory.

Prosecutor Jerome Wilcox questioned him on the effects of bright lights saying: "Do you need to rush out and go to the loo when you are in bright sunshine?" Williams replied: "No, not really."

A video of his visit to the loft was played repeatedly to a jury of seven women of five men throughout his five-day trial and showed Williams striking up a merry whistle after he had relieved himself.

The court heard Williams told a trading standards officer who was posing as the householder one of the valves was faulty while the other was old and needed replacing even though the film showed he did not check the valves until after they had been removed.

Recorder Rebecca Brown told Williams' lawyer that she was considering "all sentencing options" and the case crossed the custody threshold. The case was adjourned for a pre-sentence report.