More and more people are being targeted by firms cold-calling them to buy land they say is ripe for development, the BBC has learnt.
Many are persuaded to pay tens of thousands of pounds for land which is unlikely ever to be built on.
The Financial Services Authority (FSA) said it was investigating about 20 such schemes.
The City of London Police's Economic Crime Directorate said what it had seen so far was the tip of the iceberg.
William McNaught, from Yorkshire, was contacted by The Property Partnership three years ago and persuaded to pay £101,000 in order to buy eight strips of land in different locations around the UK.
He said he was convinced by the high returns which were promised.
"They were so convincing. The broker told me the investment would achieve a profit of 100-130% in a period of 12 to 18 months," he said.
Radio 4's Money Box has investigated a strip of land Mr McNaught bought near Towcester in Northamptonshire for £10,000 in September 2009.
Instead of being close to development, the land is within the boundaries of the historic Easton Neston Estate and the local council has served further restrictions which mean not even fences or agricultural sheds can be erected.
John Townsend, the councillor responsible for planning at South Northamptonshire District Council, said the area was protected to prevent any sort of development.
"It is in open countryside, it is in a conservation area, there are endless reasons why I think it would very unlikely that planning permission would ever be given," he said.
"Nothing can be put here, they cannot put up any fencing, they cannot put up any sheds or huts."
Craig Bees, a director of the local estate agency Bartram and Company, was asked by Money Box to try and value one of Mr McNaught's strips of land. He believes it is worth a fraction of what he paid for it.
"I would describe it as a postage stamp in the middle of a park. It has no access to it and it is too small to build anything meaningful on," he said.
"It has very little or no planning potential. The plot is worth in the order of £75."
Mr McNaught admitted he did not make local enquiries before agreeing to buy the land, something he now bitterly regretted.
"I have been foolish and I am now paying the penalty for that foolishness," he said.
The Property Partnership is a trading name for the firm Ultraclass Limited. Money Box asked The Property Partnership to comment on the land it has sold to Mr McNaught but it has not responded.
The City of London Police's Economic Crime Directorate said Mr McNaught was not alone in having been tricked into handing over large sums in order to buy land which had minimal value.
Detective Chief Inspector David Clarke said this was a growing problem.
"There is a significant amount of activity within the law enforcement community ongoing at this point in time to assess how big the problem is. I believe what we are seeing at the moment is only the tip of the iceberg," he said.
The FSA said it had closed down five land investment schemes in the past year in which £42m had been invested. However it can only act if it is able to prove that a firm is effectively running a collective investment scheme in which it promises to liaise with potential developers on behalf of clients.
Jonathan Phelan, head of unauthorized business at the FSA, said the organization was doing its best to clamp down on the problem.
"Where you have a collective investment scheme, we can get involved. We would estimate it to be around at £200m problem. We have got 20 firms under inquiry," he said.
"What we are seeing now is much more criminal. They are not even trying, they know they are buying land which will never get planning permission."
He urged anyone who believed they had been a victim to come forward.
"Please, do come to us because there are a dozen, a hundred, a thousand people who are going to come after you and lose similar amounts of money. We really need you to tell us," he said.
Mr Assemakis's firm The Property Partnership should not be confused with the Surrey based building services firm Land Investments UK Ltd trading as The Property Partnership.
BBC Radio 4's Money Box is broadcast on Saturdays at 1200 GMT, and repeated on Sundays at 2100 BST.