The “unusual fraud” was confirmed by detective work by one of the men’s employers using GPS tracking technology on the employee’s company van.

The deception by the two men was uncovered after an engineer went to Our Lady’s Abingdon school to start plumbing work but could see that asbestos material had been left, putting him and others at risk of exposure to dangerous fibres.

He reported it to the Health and Safety Executive which investigated and brought a prosecution against both men.

Oxford Magistrates’ Court heard that Richard (Ricky) Gray, an asbestos analyst, of Hoddesdon, Herts, and David Gray (no relation), of Botley, Oxford, a supervisor for a licensed asbestos contractor, had committed the offence on Sunday 25 July 2010, probably just to escape a few hours’ work.

HSE found David Gray’s employer, Maylarch Environmental Ltd, had been hired to carry out an environmental clean of the area affected by asbestos between 21 and 25 July.

Ricky Gray’s employer, environmental consultants Tersus Ltd, had been contracted to provide a final independent assessment of the clean-up on 25 July, which is required for all asbestos removal work.

On 27 July, H&E Engineers from Oxford arrived at the school to carry out boiler work.

Supervisor Trevor Benfield was immediately concerned that asbestos materials had been left in a poor condition and alerted HSE.

During the investigation HSE discovered that Tersus had believed their assessment had been properly signed-off as it had a report from employee Ricky Gray. However, when told of the conditions found at the school, it carried out its own internal investigation.

Tersus used GPS tracking and found that Ricky Gray’s van had been driven to a service station at Junction 8 on the M40 and back to his home address on 25 July – not to the school site where the assessment was due to take place.

He later admitted he had met David Gray there and together they had fabricated the clearance report to make it look as though the assessment had been carried out.

Ricky Gray of Hoddesdon, was fined £4,000 and ordered to pay £1,000 in costs; and David Gray of Botley, was fined £1,000 with £250 costs after both pleaded guilty to a breach of Section 7 of the Health and Safety at Work etc Act.

After the hearing, HSE Inspector Andrew Moore said: “This was an unusual fraud, the first of its type that I am aware of. It was only detected thanks to Mr Benfield’s knowledge and perseverance, and the use of GPS technology.

“It was also a serious fraud as it may have exposed other workers coming on to the school site to the very real dangers of inhalation of asbestos fibres.

“I can only have an educated guess at what motivated these two to collude in this fashion. For Ricky Gray, it was his last day at the company and it was a Sunday.

“For David Gray it was perhaps also the temptation of finishing work early as contractors have to wait for analysts to finish their assessment on site – and stay to put right anything that needs action.”