While £2.7bn is staked on illegal sites online – impacting every area of betting and gaming from online poker to horse racing - the study suggested up to a further £1.6bn could be being staked in-person at illegal gambling dens.
Standards body the BGC said balanced regulations and stable taxation is the best defence against the black market.
Betting and Gaming Council CEO Grainne Hurst, said: “This shocking report exposes the unnerving true scale of the growing, unsafe, unregulated gambling black market.
“From online gaming, to betting on sports like horse racing, millions of customers are being driven into the arms of pernicious black market operators. These people don’t care about player safety, don’t want to pay their fair share to support sport and don’t pay a penny in tax.
“By failing to adhere to the stringent standards set by the Gambling Commission, unregulated operators in the unsafe black market can make bigger offers, grant customers total anonymity, and promise the freedom to gamble without any controls or safety measures, unlike BGC members.
“Worst of all, these sites are making a mockery of the rules set up to protect the most vulnerable by aggressively advertising their services to those who have self-excluded.