The Tesco site shows how much the pass will cost using Clubcard vouchers.
When you redeem vouchers for Now TV and many other services such as Railcards and magazine subscriptions they have a reward equivalent to three times the voucher value. So for example if you exchanged £5 of Tesco Clubcard vouchers for Now TV credit you would get £15 of Now TV Credit which you can used to purchase passes etc.
From this it’s easy to see the Entertainment pass which is £7-99 would cost a third of that in Tesco vouchers (£2-66 x 3 = £7-99).
If you only exchanged £2-50 in vouchers your Now TV credit would be £7-50 and you would pay the difference of 49p with your usual payment method.
