Image caption Card trick: victims watch while their bank cards disappear on the doorstep

Police are investigating a frightening new variation of card fraud, which tricks people into handing over all their credit and debit cards on the doorstep.

Victims are persuaded to cancel their cards, but when they try to phone their bank to do so, the person they end up talking to is the fraudster himself.

He or she convinces them to hand their cards over to a courier, who calls at their door within the hour.

Police as far apart as London, Manchester and Glasgow are investigating similar cases.

A nursing manager with the NHS is among those who have been tricked within the last two weeks.

The woman, who lives in north London, did not want to be named.

Hello, is that the Halifax?

Yes. I can help cancel all your cards, even with other banks. says a convincing voice at the other end

"I felt totally violated," she told the BBC.

"It was like being burgled. It is that same sense that your privacy at home has been invaded."

She and her husband ended up handing over four debit and credit cards, and only realised they had been conned a day later.

By that time, the fraudsters had spent £1,200 on their accounts.

The scam

The con began when the nursing manager received a phone call from someone claiming to be a staff member at the Apple store in London's Regent Street.

He explained that her grand-daughter was in the store, trying to spend £1,000 on a card he thought belonged to the hospital manager.

He said the police had been called, and put the phone down after saying that the customer had run off.

The woman immediately tried to call her bank, to get the card cancelled.

But unknown to her, the fraudster, or one of his accomplices, simply stayed on the line, meaning that while she thought she was calling her bank, she was again speaking to a conman.

"Hello, is that the Halifax?" she asked.

"Yes, how can I help?" said a convincing voice at the other end.

The supposedly helpful assistant went on to explain that, under a new scheme, the woman could now cancel all her cards in one go, even cards belonging to rival banks.

Image caption Hanging on the line. But do you know who you are talking to?

She was then asked to dial her PINs into the telephone. She did so not just for her own bank cards, but for her husband's as well.

The fraudster explained that the cancelled cards would then be collected by courier.

For security reasons, she was told to ask the courier for a code number.

When he turned up on the doorstep within the hour, and repeated the correct code, she handed him an envelope with four perfectly valid credit and debit cards.

The fraudsters now had four cards, and four PINs to match.

"I thought it was odd at the time that I got straight through to the bank," said the woman.

"Afterwards you feel so stupid that you were conned, but at the time you are in a panic."

Changes

If you receive a phone call that seems suspicious, end the call immediately and don't give out any information Action Fraud How to protect yourself from fraudBBC Watchdog: Credit card fraud

At the moment, when someone makes a telephone call, it is possible that the line can stay open, even though the person receiving the call has hung up.

When the person receiving the call picks up the phone again, they will not get a dialling tone. But in stressful circumstances, they may not notice.

The fact that they then dial a number on the keypad makes no difference to the line, which remains in place.

The telecoms regulator Ofcom is working with the industry to get this changed.

Talks are currently taking place to see how easy it would be to alter the necessary technical systems, and to establish how quickly such changes could be made.

"Ofcom is extremely concerned that telephony network features are being exploited in this way and we are working as a matter of urgency with the Metropolitan Police and the fixed-line telephone industry to put a stop to this particular criminal activity," a spokesman told the BBC.

Advice

Criminals are making in excess of £50,000 a day from this type of crime Det Insp David Peritt, Police Scotland

The scam is similar to another fraud well-known to police, in which victims are phoned by someone claiming to be from their bank. For security reasons they are asked to ring back. But again, the fraudster simply stays on the line, and receives the call back.

The victim is told their card needs to be returned to the bank to be changed, and they are to give it to the courier on the doorstep.

In Glasgow, Police Scotland (formerly Strathclyde Police) have warned that criminals are now making tens of thousands of pounds from the scam every day.

"Our ongoing enquires into such scams have revealed that some criminals are making in excess of £50,000 a day from this type of crime," said Det Insp David Peritt.

"These individuals are highly organised using sophisticated equipment to defraud innocent people of their money," he said.

In Manchester the police are warning that the fraudsters are also posing as police officers.

But again they tell their victims that their cards need to be collected. In two recent examples, in April, victims were asked to hand their cards over to taxi drivers.

Police say the average amount lost by victims is £4,000, although in most cases the bank takes responsibility.

Over a two-year period, up to Christmas last year, the Metropolitan Police say 93 fraudsters operating such scams were charged, having stolen a total of £2.4m from their victims.

One had taken nearly a quarter of a million pounds.

Action Fraud, the government body which fights card fraud and internet crime, has some simple advice for consumers.

Your bank will never ask for your PIN details

Your bank will never collect your bank card

Your bank will never attend your home

Should you receive such a call, end it immediately

"If you receive a phone call that seems suspicious, end the call immediately and don't give out any information," an Action Fraud spokesman told the BBC.

"Instead call your bank from another phone or go into a branch."

In the meantime the woman who was conned did not end up out of pocket. The banks involved all agreed to cover her losses.