It is only for selected restaurants. It excludes:
PizzaExpress Ashford McArthur Glen, Barnstaple, Bath - Southgate Centre, Bath - Theatre Royal, Bluewater, Brent Cross, Brighton - Jubilee Street, Brighton – Marina, Brighton - The Lanes, Edinburgh - George IV Bridge; Edinburgh - Holyrood; Edinburgh - North Bridge; Falmouth, Jersey - St Brelade, Newquay, Portsmouth - Gunwharf Quays, Ramsgate, St Ives, Torquay, Truro, Whitstable, Windsor, Wimbledon Village on the 12th of July, Worthing or at live music rooms.
If your local restaurant isn't on the list above, it's all good! Just head here: https://www.pizzaexpress.com/offers Enter the restaurant you would like and choose the 2 for £10 offer, then fill out your details. They also have other offers in various locations for 2 or 3 course meals.
Hope this helps!