Only 2nd post so go easy!
Pizza Express pizzas at Waitrose contain a voucher for 20% off your total bill. This is NOT the same as the Sunday Times offer as there are no restrictions as to when it can be used other than the closing date of 7th December. Note that you also get 20% off drinks which is very good IMHO. Price that I have shown is for a Margharita - other probably vary.
Not too sure of start date and it may well have been in the shops for a while and it may also be on offer in other supermarkets flogging these pizzas.