Banned from the bookies
Bookmakers are "refusing to take bets" from successful gamblers.
Some clients have told the BBC they've had their betting accounts closed or their bets "restricted" following wins.
Bookmakers say they limit bets from a minority of customers to ensure good odds are available to everyone.
Neil Smith, a teacher from Yorkshire, says he's had around 450 online accounts closed. One bookmaker restricted the amount he could bet, and only allowed a 10 pence bet on a 4/1 horse. He said: "They will just say: 'Sorry our traders have deemed your betting pattern to be unprofitable and we're a business'.
"They shouldn't be advertising a product that's not available to everybody. The flipside of this is they are trying to squeeze money out of people who they are know are profitable. If you're good, you can't win long-term, it's as simple as that."
Campaigners are calling for the gambling authorities in the UK to force bookmakers to accept all bets up to a limit - a move which has recently been imposed on bookmakers in Australia - and make it clear to all players that restrictions may be imposed.
Peter Ling runs the Secret Betting Club, an independent gambling advice service. He says the bookmakers are using ever more sophisticated IT to identify likely winners, and is campaigning for a more equal playing field.
"Five years ago it used to be a badge of honour for serious punters to be restricted, and you would have to win some substantial sums to get a letter or email like that," he said. "But these days it's all too common.
"And it's not just people like me or my members, but your regular Joe Punters who are having the occasional bet, and are having some success, are finding themselves restricted."
He surveyed his 850 members to find out who had accounts closed or "restricted" to a small percentage of the stake they wanted to wager. Three quarters of respondents reported that one company sought to regularly restrict bets to a few pounds. Half said another firm had closed their accounts.
5 Live Investigates spoke to gamblers who suspect sophisticated software programs which are used to combat fraud are also being used to track people's betting patterns online or check whether they are using comparison sites.
Two told the BBC they had accounts closed with one bookmaker before they'd even put a bet on. The Association of British Bookmakers said they were unable to comment on the allegation.
5 Live Investigates has been told some High Street shops are also on the alert to identify the smartest gamblers and restrict the bets they can put on.
Neil Smith says he has been banned. One shop told him it was because they'd had a handwriting expert compare his betting slips with previous winning bets.
One shop manager who wished to remain anonymous said the company encouraged staff to screen-out successful gamblers: "They grade. If they are a serious backer of horses and clearly know what they are doing with the odds then we don't want them at all - the orders are 'get rid of him or let him have a have a few quid on the starting price only'."
Customers have told 5 Live they believe the cooling attitude to those punters who follow the odds and apply mathematics to their wagers, is directly connected to the success of fixed-odds betting terminals and other casino-style games of chance online.
But the industry insists they are just trying to be fair to the ordinary punter by restricting a small number of what they call "professional" gamblers.
The BBC asked firms about the practice of restricting bets but most declined to comment.
However, Paddy Power said it managed financial risk like all businesses and had a number of checks and restrictions in place to prevent certain bets being made.
"We take a 'one-for-all' rather than an 'all-for-one' view, so for instance if we're prepared to lose €2m (£1.5m) on an event, we would much prefer to lose €2,000 to 1,000 different customers rather than €2m to one individual," a spokesman said.
William Hill insisted the vast majority of their customers could bet what they like when they liked, but to provide competitive prices to its recreational customer base it sometimes restricted bets from a small minority of customers, mainly professional gamblers.
Other bookmakers declined to comment on their policies.
5 Live Investigates is on BBC Radio 5 Live at 11:00 BST on Sunday 18 October. Listen online or download the programme podcast.