No, this is no longer necessary. You can use any Halifax credit or debit cards worldwide now, without having to give the bank a heads-up beforehand. Halifax does state, however, that you should ensure it has an up to date mobile number to contact you on (in case it's worried about suspicious card use). Always carry a back-up means of payment when you're abroad, and if you need to contact Halifax while you're away, you can call +44 1733 573189.