Betfair said it is to withdraw from the Greek market over new regulations that it called protectionist and inconsistent with European law.
Earlier in November the Greek Gaming Commission announced there would be financial penalties and criminal sanctions against gaming operators that continued to operate in the market without a permit.
Betfair said it had not applied for a permit due to questions over the legality of the Commission's decision.
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It added that the associated financial conditions attached to these permits, which could include payment of taxes on historical revenues, made the market "economically unattractive".
Before its decision to withdraw from the market, Betfair had expected to generate £13m of revenue and £7m of profit from the Greek market in the current financial year.
"Betfair has been working with the Remote Gambling Association to achieve legislation that allows fair competition in the market," the firm said in a statement.
"It is disappointing, however, that the European Commission has, despite previously stated intentions to the contrary, not taken effective action to prevent protectionist behaviour."
