Police have edged closer to catching high-tech robbers who have targeted Jewish jewellers in north Manchester after one victim helped officers target the criminal ring. He found his car fitted with a sophisticated tracking device and alerted police.

Hundreds of thousands of pounds worth of diamonds and jewellery has been stolen in a three-year criminal operation which had been planned since 2007.

In June last year, a self-employed Jewish diamond dealer was targeted when £220,000 worth of jewellery was stolen from his car in a high-speed coordinated attack on King's Road in Prestwich. In September 2010, £150,000 worth of diamonds was stolen from another jeweller in the heart of the Jewish neighbourhood in Broughton Park.

But on Tuesday one accomplice, Shaun Flanagan, 54, of Blackley in north Manchester, admitted to conspiracy to steal at Manchester Minshull Street Crown Court and was jailed for four years. He used sophisticated tracking devices covertly fitted underneath jewellers' cars and admitted to tracking vehicles over a number of days.

He was caught after a third jeweller, who was carrying £200,000 worth of pearls, believed he was being followed and alerted police when his car mechanic found the tracking device on his vehicle.

‘This was by no means an amateur operation’

Mr Flanagan did not admit involvement in the raids but police searches on his house recovered a night vision device, radio scanners, a glass hammer, jewellery scales, an electronic gemstone gauge and papers relating to jewellers.

Greater Manchester Police said an ongoing operation was underway to catch the remaining suspects.

Detective Sergeant Simon Akker, of Salford CID, said: "Flanagan identified targets who he knew had access to valuable jewels and meticulously stalked them. This was by no means an amateur operation."