Sainsbury's home delivery operation has been severely criticised in terms of road safety after a reporter worked under cover as a driver for four months.

Tim Blakemore, managing editor of Commercial Vehicle Engineer, worked as a driver from the Water Lane store in Farnham, Surrey, between November and March. He was allowed to carry out deliveries before completing a one-day training and assessment course with the AA's Drivetech division a ­requirement for all drivers and before anyone at the store had seen him drive.

Blakemore claimed he was told to replace a headlight bulb on his van himself and was given a bulb for an entirely different model. He also questioned the transport management qualifications of its home delivery managers and the reporting of defects that arise while on deliveries.

A Sainsbury's spokesman refuted the claims and said a comprehensive set of safe working practices was in place for online vehicles. "All are safety-checked by the driver on a daily basis and release-signed as safe prior to departing the store," he said.