As many as 5.8 million people a month visited online gambling sites from April to September, according to figures seen by Panorama.
And those statistics from the internet media and market research company, Nielsen/Net Ratings show that in May there were more than six million.
But research by the Gambling Commission for the government found only one million regular UK online gamblers.
An addiction expert predicted up to one million a year could become hooked.
Professor Jim Orford has criticised the government for being "naive" and "playing dice" with people's health by liberalising gambling laws.
It is currently illegal to run an internet casino gaming operation in Britain but that is about to change.
The Gambling Act which was passed in April 2005 and comes in to force on September 1 2007 will allow online casino companies to set up in the UK from September next year.
The government has created the Gambling Commission to regulate gambling. It will vet sites and give official approval to those with the best working practices.
Operators will not be allowed to target children and must keep customers informed about how much money they have spent.
Key staff, such as managing directors and finance managers, will be checked for links to organised crime.
The minister for sport, Richard Caborn, said: "We have, I believe, acted responsibly in bringing an act onto the statute book which has three basic principles on which it is based.
"Protecting the vulnerable, keeping it crime free and making sure that those who have a bet will be paid out and it¿ll be a fair bet.
"That is what it is predicated on because we believe that gambling is now part of our leisure industry."
But psychologist Professor Orford who works at Birmingham University said: "Gradually we're going to realise it's a much bigger problem than we thought.
"More people are going to know friends and family members who've got problems. Health authorities are going to be under pressure to provide treatment.
"We could be talking about a million people affected by it in any one period of 12 months, and that begins to put it on a par with drug addiction problems."
Panorama reporter Declan Lawn gave $2,000 of his own money to professional gambler Matthew Hopkins to find out if he could double it at online poker games which are played in US dollars.
Two years ago 20-year-old Matthew packed in his part time job at his local fish and chip shop in Camarthen to play internet poker full time. He currently earns up to $30,000 a month.
But Panorama also follows the story of 24-year-old Sharna Baker who stole almost half a million pounds from the merchant bank where she worked to feed her habit for backing horses on the internet.
Panorama: Online Gambling: Britain's New Obsession was on BBC One on November 26 2006.