Jack Conn, then a supervisor with a Medway company licensed to remove asbestos, was spotted working unprotected at the site at Canterbury Academy on 30 May 2013 by an HSE inspector.

Conn was seen walking around inside the sealed enclosure without wearing his essential respiratory mask, and with the hood of his protective overalls down.

A second worker could be seen removing the asbestos materials but with the correct personal protective equipment in use.

Canterbury Magistrates’ Court heard that on arrival at the school the HSE Inspector saw the thorough and correct preparations the firm had put in place, which included a fenced-off site compound with restricted access warning signs; a decontamination unit with three separate cleaning areas and the sealed boiler house with a three-stage air lock.

Looking to find someone in charge, the Inspector went down to the basement where work was underway and viewed what was happening inside the sealed enclosure on a CCTV monitor.

She saw Conn without his respiratory protection and tried to get his attention by shouting through an airlock.

When that failed, she rang the company telling them they needed to get the worker out of the enclosure.

She filmed some of the CCTV footage before the firm managed to make contact with the site and the supervisor was told leave the enclosure.

HSE told the court Conn later admitted his respiratory equipment was in the enclosure with him, on the floor, and that he was aware of the risks and the duty to wear it.

He also confirmed he had undertaken the training to be a supervisor.

Conn, 23, of Upnor, Rochester, Kent, was fined £1,000 with £1,500 towards costs after admitting a safety breach.

After the case, HSE Inspector Nicola Wellard said: “It really does beggar belief that a trained supervisor with a licensed company, fully aware of the very real dangers associated with exposure to asbestos, could then casually disregard those dangers and work in a contaminated environment.

“Jack Conn, as supervisor, should have been setting a high standard to other employees and being seen to take seriously the precautions necessary to control the risks to himself and others.

“It was an obviously flagrant and deliberate breach. I hope he will not come to regret it in years ahead.”