The tunnel pound was 'assumed' to be 14 day before as there wasn't any signage to say otherwise. If there was a 48h sign at the southern end I don't remember it, but if there was then why wasn't a sign put at the Northern end? How did people coming in from the tunnel end know?
Anyway that's all in the past now. I personally think that the £25 notices are aggressive and send an unwelcome message to visiting boaters.
As I said before, people may worry that in an emergency or breakdown and have to leave the boat for a few days, they will run up a big bill.
Unfortunately it's the nice people who worry about doing the wrong thing who are being inconvenienced. Those who don't give a toss or/and aren't afraid to just play by the law let it go over their head.
I'm sure if the £25 fine bit was removed from the 48h signs it would encourage more boaters to stay in SB. Why not try it for a year and see what happens?