Little update: Turns out the paper was pasted on (with some nuclear fusion glue) but had a slightly vinyl finish.
I left MrsSb to do the first 2 hours during which time she managed about 6 feet of border then retired to the sofa muttering rude words.
I then took a sharp knife and slashed the border diagonally about every 2″ then sprayed with warm water with some fabric softener in it. This helped but the best solution was for the last wall – spray with water, leave for 15 mins, tear off top layer of paper, spray again and then go for a walk on the beach.
When we got back the base layer just came straight off.
Prob took 4.5 hours to do the lot – I hate borders 👿
Oh yeah… filling knife was too flexible, stripping knife was better.