Another colorful expression from that British movie I mentioned earlier. The context of the quote here is that there are these guys trying to smuggle ecstasy pills, and there's another guy hosting their meeting in exchange for a below-the-table bribe, though he's not directly involved himself. The host is anxious and wants them to move on quickly from the spot he's providing, as he's a civilian -- he doesn't "want to get nicked." One of the smugglers retorts back to him, "Don't worry, you'll be in your whack", in what sounds like a Cockney English accent.
So my questions are: What does this phrase mean, exactly? What does the whack add to the meaning? Is it common amongst certain types of British English speakers?