At the start of referendum night Remain was 2/9. At the close of the polls in the US Election Hilary Clinton was 1/10. The bookmakers are good (and they always win in the end) but they are not perfect - especially when it comes to public votes. Given that Danny Mac is only 2/5 and that almost all bookmakers have miniscule maximum stake limits on "fun" bets such as SCD I would expect Danny to win, but it's by no means a foregone conclusion.