Can't help you with Up North specifically, but Charge Your Car
seems to be compatible with a number of networks, and I think of them as being Northern-biased they also charge for use after-the-fact (monthly I think), which gets my vote ... the accuracy of their map is a joke (in fairness I haven't checked if extensively ... but e.g. the charger I used in York was over a mile away from the marker on their map ...) so use Zap Map
to get more accurate location,and also User feedback on whether its operational or broken ...
My advice FWIW:
If a Supplier has an APP for phone, and ability to use it without having to have actually put down a 20-quid deposit beforehand (albeit that you might have had to register a Credit Card) then you might as well do that. Install the App and register before you leave home to ensure you have good WiFi
If you are going to charge with a particular Supplier often then get their RFID token - that will let you charge even if you cannot get a mobile phone signal / use the APP at their pump for some reason. Likely to connect more quickly too. (The APP I use for Polar takes about 5 minutes for the time-to-connect and the time-to-disconnect, its ridiculous!)
Also reasonably likely that you will be able to phone them, if you are stood at a charging post and can't get it to work, and they will activate it remotely. So worth having their support phone number with you (in case there is no data-network for APP)
I have used 3rd party charging so rarely that it would have made zero sense for me to pay a monthly-sub, or even to buy an RFID chip (despite what their sales people were absolutely convinced would be best for me
). Rollout of new Tesla Superchargers means I need 3rd party less-and-less ...