I took the kids to Sea Life for their birthday armed with 2 Entertainment Book BOGOF vouchers. I guess the standard practice is surrender them to the front desk and get your 2 for 1 tickets. To beat the queue, I used the self serve machine, entered the promo code of the ticket 1207 and didn't have to surrender or show my vouchers.
At entry, they just beeped by tickets and didn't request the voucher (as above, I assume you would normally surrender the BOGOF at the counter when buying)
50% discount and still have the vouchers. The BOGOF code was 1207 if anyone would rather pay what the aquarium is worth :)
Thanks for sharing!