Vulnerable people are being warned about an infamous scam which has started operating in St Albans.

Reports of aggressive door-to-door salesman, known as Nottingham Knockers after the location where the scam originated, have been reported to St Albans district council (SADC) and Herts Police are aware of an incident involving them in Harpenden.

The cold-callers are often peddling overpriced household goods and pretending to be ex-convicts on a rehabilitation scheme, but may be gathering information for future crimes.

The hoaxers might carry fake identification cards to lure in victims and inspect the condition of any bank notes they receive to make assumptions about the household.

Crisp notes indicate a higher turnover of cash and musty smelling notes mean it was kept alongside more money.

Addresses which have been marked as lucrative may be sold to other dodgy tradesmen.

A 61-year-old St Albans woman, who wished to remain anonymous, unwittingly bought microwave cleaner and a pet hair remover from a cold-caller with an identification card: “It seemed easier to buy something then to argue with him,” she said.

“I didn’t think he was confrontational, I just thought he was someone who was down on his luck and it was very easy to buy something from him and he would go on his way.”

Once she had agreed to buy one thing, she was persuaded to buy more to make the price a round number - a £20 note.

In the future she said will scrutinise the caller’s ID card and possibly ask more questions.

Elderly people are most at risk, especially if the scammers become confrontational and aggressive.

Policy, partnerships and economic development manager for SADC, Helen Wright, said: “A resident contacted our Community Safety team last week to complain of an approach by unsolicited door-to-door sellers.

“Our advice in these instances is not to buy anything, call the police on 101 to report the incident and warn your neighbours to do the same.”

Sellers should also be reported to Herts county council’s Trading Standards department through the Citizens Advice consumer helpline on 03454 04 05 06.