Would a betting site refuse to pay me if i won 3 million GBP?

Paddy power, the site I will be making the bet on. I know you may think it's a long shot (winning 3 million), but I like my chances. I don't know. I can just imagine them finding a reason why not to pay, or canceling the bet when it's down to the last few. By "last few" I mean the last few bets on the parlay. I don't know much about the company. I know they're quite a big company, and quite a well known company, but I'm sure losing 3 million would seriously hurt them.