The Health & Safety Executive has prosecuted a workman for poisoning an elderly couple with carbon monoxide in their Edgware home.

Dermot Healy of D Healy Plumbing & Heating in Hertfordshire pleaded guilty to breaching Regulation 3(3) of the Gas Safety Regulations 1998 at two separate addresses, as well as Section 3(2) of the Health and Safety at Work Act 1974.

Healy was fined £500 for not being registered while carrying out gas work and for not holding Competence Certificates, and was ordered to pay costs of £1,500 at the City of London Magistrates' Court.

The Edgware couple's home had a gas-fired Lennox warm-air unit from 1961, despite it being condemned by gas engineers 14 years before the incident, which took place in 2007.

Healy had been asked to re-commission the unit and undertake annual service checks. Among his handy-work was the installation of a plastic vent cover.

Following the incident, an investigation showed that the air unit cupboard had insufficient ventilation and the flue was also of an insufficient length, with two 90º bends restricting the escape of exhaust gases to the outside. Negative pressure in the cupboard resulted in gases being drawn down into ducts in the unit.

HSE inspector Charles Linfoot said: "The couple in this instance were lucky, but the outcome could so easily have been a tragic one."

Visit Gas Safe's website, www.gassaferegister.co.uk, for details of how to register.