[the telegraph] John Penrose, the minister responsible for gambling policy, said the regulations would be based on the "point of consumption rather than production".
Licences granted by certain jurisdictions are currently treated as if they are issued by the UK.
While the proposals from the Department of Culture, Media and Sport did not mention taxation, its statement said offshore operators are not "bearing a fair share of the costs of regulation".
Evolution Securities analyst James Hollins said "the statement firmly implies" the legislation will include taxation.
He said the most likely outcome was a 15pc gross profits tax rate for online operators to match the level applied to land-based gambling, which would "impact William Hill and Ladbrokes by about £25m to £30m per annum".
Ladbrokes chief executive Richard Glynn said the proposals were "welcome" but a more "comprehensive solution" was required.
William Hill shares fell 3.7pc and Ladbrokes lost 1.7pc.
Offshore bookies face crackdown