Cork isn't in the UK. That's your problem.
If T-Mobile is in Ireland, you can probably get top-up cards and use them with T-Mobile UK. Most of the carriers that serve multiple European countries allow the use of top-up cards from any of the countries to be used.
Another option is to get your top-ups in Northern Ireland, which is part of the UK.
CA: SaskTel, Wind postpaid; Rogers, Bell postpaid iPad flex plans; US: T-Mobile postpaid data, prepaid voice; PureTalk (AT&T MVNO) prepaid voice/data; AT&T prepaid iPad plan
Hardware: Too much but notably iPhone 5, iPad Mini Retina LTE, Moto G LTE (N.A. version), iPhone 4. All unlocked.