British bank to
Irish bank -
21 working days.
BACS transfers from British banks to Irish banks and vice versa - possible in theory, haven't had a single one actually go through smoothly yet ("the bank lost your salary" is still one of the most surreal conversations I've had with an agent).
Banks are bastards. They are blood sucking parasites who should be wiped from the face of this earth for the betterment of humankind. Trust me, get rid of banks and there will be world peace and an end to famine worldwide.