Dangerous lorries could still be operating on the streets of south west Hertfordshire, police have warned, 17 months after they cracked a bogus licence scam.

On Friday, John Plummeridge and Philip Cameron were found guilty of fraud, having headed a criminal network which organised fake applications for large vehicle licences.

The pair’s arrest, in May last year, came after a painstaking 14-month police investigation - codenamed Operation Cluedo.

However, police this week warned: “There have been – and still could be – dangerous vehicles on the roads both here and abroad as a direct result of the actions of this pair.”

After guilty verdicts were handed to Plummeridge, 48, from Watford, and Cameron, 62, from Bushey Heath, Detective Superintendent Glyn Jones, who ran to operation to expose them, said: “These men abused a system put in place to ensure everyone's safety with such a degree of arrogance that they believed they would never be caught.

“The scam they were running meant badly-maintained lorries were on the roads and that can result in serious injury or even death.”

The scam was exposed after the investigation found the two men had organised the fraud operation through a PO box number in Watford.

Basildon Crown Court heard the two men, who had no formal qualifications, had claimed to be working as “transport consultants”, advising haulage companies on obtaining heavy goods licences.

They had, however, been producing applications with false details to get licences fraudulently.

This led to a large number of poorly-maintained vehicles coming to the attention of police, who discovered licence-holders could not be found.

Details on a large number of licences led back to the Watford PO box address.

Two companies from Hillingdon - Rino Haulage Limited and Iver Builders Merchants Ltd - were also involved in the scam, with their directors using bogus licences for their heavy goods vehicles.

Other members of the criminal gang have already been sentenced.

Thomas McKinney, 34, a director of Rino Haulage Ltd, was fined £22,000 for hiring fake licences on demand from Plummeridge.

Mohan Singh Bambra, 44, of Kingston Road, Southall, who was a director of Iver Builders Merchants Ltd, was found guilty of five counts of using a fake licence with intent to deceive.

He has been fined £25,000.

Martin John Lavelle, 36, of Castleton Road, Eastcote, was also found guilty of making a false representation to obtain a licence and fined £500.

Plummeridge and Cameron will return to court in December for sentencing.