The latest street racket to hit London is exposed today.

Westminster council says Eastern European gangs are raking in hundreds of pounds a week from shoppers and tourists in the West End.

Fraudsters, mainly Romanian, are fooling people into handing over cash in exchange for worthless metal rings. In the case exposed today a council worker intervenes to prevent the trick going ahead.

Westminster council issued the CCTV images to warn tourists and Londoners about the swindle which they say is now an everyday occurrence in Oxford Street. It works by con artists dropping a gold coloured ring next to an unsuspecting passer-by. They then “spot” the ring and make a big show of picking it up, asking the “victim” if it is theirs.

When the person says no, the trickster offers to give it to them in exchange for anything up to £20.

In the CCTV a member of the fraud gang approaches a woman at a street crossing. But after she is shown the ring and engaged in conversation, a council worker, thought to be a street cleaner, steps in and stops the con.

One shop owner said he had seen at least 50 people in the space of a week who had been caught by the scam.

Mick Smith, the head of Westminster’s neighbourhood crime reduction unit, said the fraudsters ask for cash usually claiming they need money for food.

He said: “Often they will point to a fake hallmark which we suspect they have put on themselves. Obviously when the person goes to get it valued they discover that it is worthless.

“The fact that one nearby jewellery shop alone says they have seen around 50 people in the space of a week gives you some idea as to the scale of it.” The con is said to have originated in Paris.