Concerned passers-by blew the whistle when they spotted workers on an unsafe roof of an empty industrial building in Gillingham.

Their fears were investigated by Health and Safety Executive (HSE) officers who filmed them casually walking on the surface which was clearly marked as being fragile.

An inspector said they could have been killed or seriously injured if they had fallen more than 20ft on to concrete below.

The Surrey-based company was fined £13,400 and ordered to pay £9,167 costs after being prosecuted by the HSE for placing employees in unnecessary danger at the premises in Bredgar Road.

Industrial Roofing (Surrey) Ltd had been sub-contracted to replace and repair gutters in March last year.

When an HSE inspector arrived at the site, he saw clear evidence of work on the roof without any precautions in place to prevent a fall.

After the hearing at Medway Magistrates' Court on Tuesday, inspector Melvyn Stancliffe, said: "I would like to thank members of the public who brought this matter to our attention.

"They provided clear evidence of the unsafe way in which the roof work was being undertaken, and in doing so, they may have well have prevented a fall that could have killed or seriously injured a worker.

"Work at height is inherently fraught with risk and falls remain the single biggest cause of deaths and serious injury in the construction industry."

A prohibition notice was served to prevent any further work on the roof until safeguards were in place. Employees were also ordered to undergo training at working at height.

The firm, which is no longer trading after being compulsory wound up, did not contest either requirements.