Why do Merlin Annual Pass Holders need to book?

Neither a Standard Merlin Annual Pass nor a Premium Merlin Annual Pass will guarantee immediate entry to any Attraction or any event at any time. At Attractions or events which allocate individual time slots for entry or where pre-booking is available, Standard Merlin Passholders are required to book an available time slot or pre-book their entry in advance in order to guarantee entry to the Attraction or an event, otherwise they will not be permitted entry. Entry is always subject to the Attraction not being at full capacity. Please note that Premium Merlin Passholders may be turned away from the Attraction or the event if they have not booked in advance. Please note that all time slots are subject to availability and so to guarantee a specific time slot, booking in advance is strongly recommended. Passholders are able to book an available time slot online by visiting the website, and a small fee of £1 applies.  When any Passholder has booked a timeslot (irrespective of whether they hold a Standard Merlin Annual Pass or a Premium Merlin Annual Pass), the Attraction may ask such Passholder to leave the Attraction at the end of their allocated timeslot