By Sarah Pennells
Some people have lost tens of thousands of pounds to the scammers
Gangs targeting vulnerable people with letters about bogus competitions are using legal teams to stay ahead of the law, the BBC has learned.
In what has become a multi-billion pound industry, risk assessors are also being employed by scammers, according to the Office of Fair Trading
The watchdog has told the BBC that new consumer protection laws can do little to stop the actions.
The scams, which target millions of people, earn about £3.5bn a year.
One woman has told how the scammers had targeted her ex-husband who had been left vulnerable after a stroke.
Eliana said he was tricked out of almost £100,000 by a gang who had promised him £1m.
"As soon as he'd made contact with them he was totally in their grip," she said.
"He totally gave up on life. Every morning he waited for the post to arrive or for a courier to arrive with the money so he wasted his whole day. It almost because an obsession. It was all he could think about."
"They were tenacious criminals who wouldn't give up until they'd exhausted all his funds."
This week, one of the gang, Victor Ifejika, was sentenced to a year in prison for fraud - but the police are no closer to discovering who he was working for.
"We know very little about him. He's not been the country for a long time but what we do know is that he was part of an organised gang," said Detective Chief Inspector Ian Chandler of West Surrey police.
"He was part of a group that was targeting numerous people and on this occasion he hooked the victim," he added.
Tracking the operation of these gangs is almost impossible as they work across country borders and some are large-scale complex organisations.
More than three million people are sending money off to such scammers, said Mike Haley of the Office of Fair Trading.
He said: "They're very sophisticated. They use direct marketing techniques and what they call 'suckers lists' to target the most vulnerable.
"And they use risk assessors and lawyers to make sure that they're one step ahead of us, the law enforcement agencies."
As the industry thrives - so the letters, leaflets and flyers become ever more convincing. And they know exactly who they're going for.
These prize draw scam companies will buy information about vulnerable people who may have a credit history problem - and target them, bombarding them with letters.
Often this will be the only correspondence that the victims receive.