There is a rap on the door of an end-of-terrace house, and after a while a man comes to answer it.

He is heavily-built, and might normally appear quite imposing. However, as he looks at the men on his doorstep, his face becomes frozen with fear.

They are uniformed police officers, and members of the Bristol-based South West Illegal Money Lending Team, and they inform him that he is being arrested under Section 39 of the Consumer Credit Act 1974.

The dialogue on the doorstep takes a matter of minutes. But it has taken more than six months for this moment to arrive.

Alan Evans, the regional enforcement manager for the team, explains: "We received a telephone call to our hotline on which people can anonymously report loan sharks.

"The caller identified this individual and claimed they were being threatened over money that he had lent them. We began to collate information and piece it together, which took about six months."

Police officers are moving in and out of the house in Eastville, not far from the Eastgate Centre, where shoppers with brimming trollies are in the car parks of major stores such as Tesco.

One officer brings in a metal ladder. Others emerge carrying plastic bags full of cash books and documents. Meanwhile, neighbours are watching from their windows.

"We've got a number of bank statements from his loft, although we had these already from his bank," says Mr Evans.

"Loan sharks tend to be meticulous individuals, and prefer keeping information on paper rather than in a computer. The amount of money involved in this case appears to be around £50,000."

The joint operation between the South West Illegal Money Lending Team and Avon and Somerset Police will mean an unexpected Christmas gift for those supposed to owe money to this alleged loan shark.

They will now know that they may not have to repay their debts. Mr Evans points out that loans from loan sharks – which can amass huge interest rates, sometimes of 500 per cent – are not enforceable anyway.

"You don't have to pay a debt to a loan shark, as it is an unlawful loan and therefore can't be enforced in the courts," he says.

"But most people are unaware of that, and we've come across people who have been paying money to loan sharks for years.

"We've seen parents who have become dependent on loan sharks, and in turn their children have because, to them, it's the norm."

Despite the threatening reputation of loan sharks, an increasing number of people are expected to be drawn to them this Christmas.

Many of them are people for whom going to Eastville and shopping for Christmas presents with a credit card would be impossible.

Mr Evans explains: "People who go to loan sharks have usually been excluded from legitimate borrowing. Maybe they don't have a regular income, or they're already in debt, or they have literacy difficulties."

Yet the recession has meant loan sharks have also begun attracting new types of client.

"Now it's right across the board and it's not just individuals. Loan sharks are lending to businesses that can't get credit, and they're taking over those businesses when they don't get paid back. This gives them a legitimate business, and opportunity to extend their criminal empire."

The South West Illegal Money Lending Team, which was set up in March 2008, has also discovered loan sharks do not just lend money.

"Sometimes they provide families with computer consoles or flat screen TVs for Christmas, and the problems come when they have to pay for them," says Mr Evans.

"The loan shark will then lend them money to pay for those goods, and people then get pulled further into a lifestyle of debt dependency and become hooked."

Finally, a 48-year-old man is escorted from the house to a police van and taken to Trinity Road Police Station, where he is later released on bail pending further inquiries.

"The hotline is working, there's no doubt about it," says Mr Evans.

"We're expecting it to go crazy after Christmas when people discover the true cost of borrowing money from loan sharks."

The hotline for reporting loan sharks in Bristol and the South West is 0300 1234 247.