CORGI, the gas safety watchdog, said appliances should be switched off if there is any chance building work may have jammed a flue, and a check carried out by a registered installer before switching on again.

Head of safety promotion, Dan Caesar, said: "When employing a tradesperson to carry out work on your home, ensure your flues and ventilation to gas appliances do not become blocked."

The warning was underlined by Paul Hoskins, an inspector with the Health and Safety Executive, who stressed tradesmen should be aware of their safety obligations.

He said: "Robert Schenker's tragic and wasteful death could, and should, have been avoided by Johnson taking straightforward safety precautions. HSE inspectors involved in this case were appalled by the poor workmanship and failure to carry out the most basic safety checks to ensure the correct operation of the flue, which directly led to the fatal incident.

"Anyone carrying out work on flues and chimneys should check they are inspected and tested sufficiently to ensure they are in a safe condition."