I've finally got around to stripping out the old carpeting the previous owner had covered the walls and ceiling in. Pulling off the carpet wasn't too bad, it was the blackened and hardened contact adhesive that remained. If it was to be recovered it wouldn't be a problem but I wanted to try and restore it to the original gelcoat. I had various suggestions such as thinners, nail varnish remover and worryingly petrol! After a few tries with various things I found a gel paint stripper from B&Q works a treat. It's branded Diall (it's not shown on the web site) I found leaving it on for at least a day or two and the glue just peels off like cobwebs, very satisfying! The gelcoat appears to be unaffected. Being a gel it sticks to the ceiling and walls with no problem.
That's good to know as my N20 walls and ceiling are covered in a horrible carpet that I've peeled away in a couple of places only to leave a thin foam backing which scrapes off fairly easily, but, as you say, leaves the hardened glue behind.
Good luck Fred. I was sceptical but it has worked very well. Just remember not to be in too much of a hurry. I was scraping and cursing at it after only leaving it for an hour, frustrated, I went home. Fortunately I only live 2 minutes drive from the marina. I returned the next day and couldn't believe the ease with which it came off.