A.
Yes, but it might be expensive. Your SIM Carrier will have additional charges for using your mobile abroad and they can be pretty extortionate especially if you're calling/texting back to the UK or using internet. If you do plan to travel with your phone either look for a SIM contract with a good deal on 'roaming' and international charges, or buy yourself a different SIM when you get to the foreign country. Free EU roaming has been one of the potential losses of Brexit, so check what your carrier's stance is.