I did it in 2006
As far as I remember I took a picture in Leeds of a metal sign with stating the full length, 127 miles, that should be the end of the ride. In Liverpool, since then, it has been extended from the original Stanley Dock to the Albert Dock, although the last bit will have to be on the road.
I did it in 3 days: Liverpool-Wigan, Wigan-Skipton, Skipton-Leeds.
Printing the permit from British Waterways is mandatory, although nobody asked me for the permit, I doubt anybody would, and I doubt if somebody had done it and I had not had it anything else would have happened. On the other side, not all the tow path is theoretically cyclable. The permit does not over the full length and in theory in some areas cycling is not allowed. As before, I doubt anybody would enforce it.
Enjoy.