A. You need a phone with NFC chip in it (actually it’s in the battery! – watch out with cheap import batteries as you can lose the functionality with some replacements).
B. The phone must have the relevant bank affiliated operator firmware.
C. You need a contactless payment enabled SIM.
It’s all tied up with exclusive deals between banks and operators basically. I’ve had several phones from Orange/EE with NFC in but told firmly by them that they will not work. The EE payment app requires the relevant phone firmware and SIM. Ask EE and they’ll say you need to buy a new phone even if your current phone is technically capable.
Google Wallet etc may be different but depends if they work without a special SIM. That may mean the phone has to be powered on and working correctly to make payments, like iPhones. So battery dies when you get to the till or tube barrier and you’re stuffed. The proper system using the SIM will work purely off the chip/antenna in the battery combined with SIM, without the phone itself powered up.