I presume the issue is that you don't have a data connection? What membership do you have? EU roaming only works on Guido and when you're in NI you're in the UK.
What should the settings for the mobile data network be when I am in Northern Ireland? I’m in the North tomorrow so I can check again to see if I can get my email working
The settings when roaming are the same as normal. Check the apn field as sometimes it changes when roaming for some reason. If it's not 48months.liffeytelecom.com then edit it, change it back to that, reboot and see if that addresses the issue. If not then you'll have to contact 48 support. See the link in my signature below.