Nigel Chester, 46, was carrying out smoke detector checks when he suffered fatal head injuries in the accident at the Premier Foods factory at Worksop, in Nottinghamshire.

An inquest jury in Nottingham heard this week that the tragedy unfolded in May when Mr Chester used a master key to unlock a first-floor door leading straight into a void.

The door had been installed 10 years earlier when bosses decided there should be a gantry above machinery at the factory, which makes gravy granules and Oxo cubes. The plan was subsequently shelved – but the ‘door to nowhere’ was retained in case it was needed in the future.

A sign by the door warned of the dangerous drop and stated that the phantom entry should remain locked. However, Mr Chester was found lying on the ground seriously injured, having apparently struck his head on a pipe as he fell. He had suffered several fractures to the skull and died in hospital the same day.

The inquest jury returned a verdict of accidental death.