The Monzo card works wherever there is a terminal, but, does ApplePay need to have a phone signal to be able to work or will it still work indoors or underground with no signal reception?
ApplePay does indeed work with no data connection info required by the NFC terminal is all located on the device.
Can confirm this. Apple Pay uses a Secure Element on the device to store and generate all the sensitive data. At a high level, the Secure Element acts very much like the EMV chip in any regular card. Therefore the device does not require any network connectivity once Apple Pay is set up.
The reason some of the other solutions require network connectivity is that they are storing the secure information server side, rather than in dedicated hardware on the device (Apple Pay) or a kind of secure VM (Android Pay).
Thanks guys. That was what I thought but having been asked the question by a friend I wanted to double check before replying to her