I have a Merlin Annual pass, for me and my family, and have booked tickets for the 2nd of October... (We have booked wrong date... lol) Anyway... We paid just £2 for each one of us. It isn't alot of money, especially considering the pays for actors, building of mazes etc. It is a pretty reasonable price I think, and it being such a fabulous park that it is
I think my simpler answer is Yes
Pre booking is required.