Parking now £15.00 unless pre booked online and then its £8.00.
Only Premium Merlin Passes get free parking.
https://www.thorpepark.com/tickets-passes/parking
I went on Friday with a bogof voucher and got a two day ticket with one free no problems and for only a couple of quid on top of the day price. I also got two days parking for the price of one as well.