It doesn't make it clear whether this relates to online, or phone and betting shop action.
When it comes to excluding "bonus abusers", the online industry seems to have an incredibly sophisticated method of looking at SEVERAL "indicators". The result seems to be that the net is cast so wide that many "innocent" gamblers get tangled up with "bonus abuse".
IF this was an online account, or even a phone account under similar terms, then this gambler could have one HELL of a case, but not how he thinks.
IF he had created what seems to be "multiple accounts", then he may well have fallen foul of terms that would have lead to any winnings being confiscated, in which case, ALL bets in the duplicate account are void, and he should receive back his "depost", just as those complainants did in the forum when WillHill online threw them off the online site for "bonus fraud".
His legal team would need to show evidence of what happens to WINNERS who circumvent the systems, INCLUDING "self exclusion". There was one incident on this forum where a player who had opted for self exclusion got back into his casino account several times, but in the end, he WON, and enough to put him back ahead overall. However, at this point, the casino decided to confiscate these winnings after repeatedly letting him LOSE while supposedly self excluded witout taking ANY action, other than offering him more promotional offers.
I doubt the courts will allow the industry to both defend voiding bets when punters win after fooling self exclusion, yet decide that LOSING bets should stand as it was the punter's responsibility to get treatment for his problem and not place any more bets.
Lastly, had this punter consistently WON with these bets, he would have been permanently excluded by WillHill (and long before winning 2Million); the big bookies CAN, and DO operate a tight system when it comes to keeping out those clever punters who consistently beat the bookies.