If you tranfer large sum of money out of Halifax bank online or on mobile app, you will receive a warning and ask you to ring this number in order to release the fund from your account. There was long waiting on the call, about 20 minutes, but 0800 numbers are free to call. Just be patient and the number is safe and legitimate from Halifax.
This number came on my screen during a banking transaction. "Additional security checks needed" it said. They said for large transactions made either online banking or through mobile app, They needed to
Make sure no one has asked or forced you to do a transaction.