A jeweller had £250,000 worth of diamond rings stolen in an elaborate sting.

Adam Alexander, a martial arts expert, said the job was planned to the finest detail and the offenders must have had inside information.

Mr Alexander, 37, is a sales representative for a jewellery firm at the UK's diamond capital, Hatton Garden in London.

He was in Brighton on Friday, selling to local shops and had returned to his blue Mercedes Benz left in Black Lion Street car park.

He carefully locked away his black fabric pilot's case containing the jewels in the car boot.

Unknown to him, the villains had got there before him, slashing a tyre with a knife as the first part of their sting.

Mr Alexander drove out of the car park but didn't notice anything was wrong until he had reached the road outside. He stopped to investigate and spotted the flat tyre.

He said: "Had I noticed it had been slashed in the car park I would have walked away. I would have smelt a rat and just left it."

There were people milling about in the street and cars moving in and out of the car park so he was on the alert.

He said: "I was conscious of the risks around me. It is something I think about all the time. I have to in this business."

He went to the car boot and took out the spare wheel and carefully locked the boot again, ensuring his diamond rings were safe inside.

When he returned to put the slashed tyre away he noticed the boot was not properly shut.

He said: "I looked inside and I just couldn't believe it. The bag was gone. It was a feeling of utter disbelief.

"I looked again, thinking I was seeing things - or not seeing things.

"I thought 'What is going on here?' There was a bloke and a young lad standing near toilets close by and I asked them if they'd seen anything.

"They said they hadn't and then both seem to disappear from the scene."

Police believe the jeweller was targeted by a gang of professional thieves who gathered intelligence on their victim's movements and his car - possibly even duplicating his car key - before carrying out the sting.

"They also knew not to take Mr Alexander on because of his martial arts training," said a detective.

The stolen jewels were insured and Mr Alexander believes they will be on the black market for Christmas.

Police are checking CCTV footage.

Detective Constable Louise Bates said: "It was a busy time of night and we are convinced someone must have seen something."

Witnesses or anyone with information should contact Ms Bates at Brighton and Hove CID on 0845 6070999.