5 of us going to see the Barbie movie at our local Odeon tonight. The price for tickets only was £48.50 
So after a little research I signed up for a tastecard for £1 for 30 days (I’ve scheduled cancelling it though as it’s £30 a year after that). I bought the 5 voucher codes on Tastecard’s site for a total of £28.80. I then entered those codes into the voucher section on odeon.co.uk. It cost £1 per ticket for the booking fee (but if you go directly to the cinema I don’t think you have to pay the booking fee, I didn’t wanna risk it as it’s a popular film).
So a total of £33.80 (including the Tastecard fee) or £6.76 per ticket saving £14.70, which will go a long way towards the snacks.
THIS ALSO WORKS FOR VUE AND CINEAMAX. But obviously you have to select those cinemas in your Tastecard account, not the Odeon. I’ll look out for other offers on the Tastecard account!