Mike Williams, owner of Castlegate News, in Castlegate, said hundreds of pounds worth of damage has been caused by the youngsters, who are aged between 10 and 15 years old, over the past few months.

The problem started during the second half of the summer holidays, he said, when gangs of youngsters began to go into the shop and were “disruptive and abusive” before stealing or damaging stock.

Female members of staff are the usual targets for the youngsters, and have been left feeling “threatened and stressed”.

“We contacted the police and they duly warned a few local teenagers and we haven’t seen them since,” said Mr Williams. “But, subsequently, it’s started to happen again with different people.”

The new gang has ripped badges off greeting cards, squirted liquid soap over stationary and torn packaging.

The last attack left the shop with a £50 bill for damaged greeting cards.

Mr Williams, who has vowed to prosecute anyone who is caught, said: “I’m becoming more and more frustrated and angry. It shows a lack of respect and shows that these children have got nothing better to do.

“I just think the parents have no idea at all of what their children are doing and would be quite alarmed if they knew. I do feel teenagers are the customers of the future. I just want them to see the error of their ways and use the shop properly.”

A police spokesman said: “Both the young people involved in this and their parents should be very aware that any act of criminal damage or theft could result in an arrest and a criminal record which will stay with you for the rest of your life.

“Irresponsible behaviour is always dealt with seriously – so be warned.