Via [coppersblog.blogspot.com] we find a Magistraite’s (Amer: “JP’s”) Courtroom Blog:
If you are facing a short prison sentence, try to get sent down for seven days on Maundy Thursday. You see, remission is one half, and three-and-a-half days is rounded down to three. Good Friday is a Bank Holiday when prisons do not release people, just as they do not at the weekend. So you will be out on the street when the court finishes for the day, having ‘served’ your seven days in a few hours.