What I found interesting was the comment that they had previously 'won' 100k, and nothing untoward was thought of it. But perhaps they got greedy and went for the £1.2m which did arouse suspicions.

So it seems to be just the same as spreadbetters - go above a certain level and you bring attention to yourself. So the rule must be to find out what is acceptable, and just keep chipping away beneath that level. And surely they would have wanted to spread themselves around a bit - 80k here and there at various casinos throughout London would easily have mounted up reasonably quickly and all without too much attention.

Divide and conquer!