European football shirt sponsorship has emerged as the bizarre battleground for an increasingly bitter fight between offshore internet gambling groups and a handful of continental regulators, determined to outlaw unlicensed online betting on their turf.

Leading the charge for the gambling groups is Gibraltar-based Bwin, already shirt sponsors at Champions League winners AC Milan. This week the group added Real Madrid to its sponsorship catalogue in a deal worth about €21m (£14m) a year - the third largest in Europe, behind insurance group AIG's tie-up with Manchester United and T-Com's deal with Bayern Munich.

The crackdown, prompted by complaints from French betting monopoly the PMU, sent a wave of panic through the league and within weeks the LFP - the game's governing body - had issued a blanket ban on all gambling sponsorship in football.

The move forced Nantes to remove Gamebookers, a subsidiary of London-listed PartyGaming, from its shirts while Toulouse was compelled to blank out 888.com from its strip. In a gesture of defiance, however, at their first match following the ban the Toulouse squad turned out against Olympique Marseille in shirts reading "???.com - censored".