Ok, Ok.
Bank holidays. We have 6 bank holidays a year. They're always on a Monday and have been around for ages. Designed originally so that bank staff could occasionally have 2 consecutive days off, Sunday and Monday, businesses soon found that they couldn't function too well if the banks were closed, so they closed as well.
It's become tradition now, and even shops only open for a few hours on Bank Holiday. Also, it's become holiday time, and is the best time not to go on the roads. Prior to a bank holiday, Friday nights see's the motorways jam packed as people stream south-west to get 3 nights away from home at a seaside resort (like WSM!) before clogging the whole thing up in the reverse direction on the Monday evening.
Englishman.