TESCO? They are not on the list of Apple Pay retailers. You sure...
Any retailer who accepts contactless payments accepts Apple Pay (up to the £20 limit). The card reader has no idea whether it's being presented with a contactless credit card or an iPhone, it just sees an RFID device.
The list of Apple Pay retailers is only relevant for purchases over £20, where you'd normally have to enter a PIN to complete the transaction - these retailers will have upgraded terminals which will allow authenticated transactions with Apple Pay (as opposed to the non-authenticated <£20 ones)