Yes, you can call international numbers if you add cash credit to your account to pay for them.
See the charges here:
https://48.ie/charges/international-calls
If the UK number is a Northern Ireland landline then you can call it using the 048 rather than 00 44 prefix and it'll be covered by your membership call minutes.
https://community.48.ie/t5/The-Knowledgebase/Calling-Northern-Ireland-landlines/ta-p/45234
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