I beleive if it is done during working hours, it shoud be instantly or within 2 hours tops.
I today had to pay someone. I made the transfer from my Halifax Current Account at approx 1300 hours and around 14:30 I had confirmation from the other person that the money was showing up in her account.
Last week I did a transfer on a Saturday night and the money reached the other party on Monday morning. It's not "fast" in the actual sense, but much faster than previously