Just to add to the throughput discussion, as advice as much as anything, Gruffalo seems to be by far and away the best ride at shifting people at Chessington. Maybe that's because there's no real way of running it at a reduced capacity like virtually all the other rides are.
The entire queue line for that ride should only take a maximum of 45 minutes even accounting for RAP and fastrack, yet it is almost always advertised as 60-120 on days like today like everything else.
That's your best bet on a busy day (besides just going home). It's the "best" in a group of terrible options, but at least it's a genuinely good ride with a slightly shorter queue than the rest. Obviously Rameses Revenge is your other good choice as the queue is always short. I'd also recommend the zoo but frankly it gets so busy on days like today that it would practically be gridlock with little chance of seeing anything, I hate zoos but on a peak day at Chessington the caged animals are probably having a better day than paying customers!