To andyman7.
I took your advice and Bingo, spot on. I started with a Peco rail cleaner but that was too cumbersome and abrasive, so I reverted to a wooden cocktail stick slanted at a 45deg angle so as not to scratch the surface. Moving it around very carefully and with much patience, I eventually removed everything that shouldn't be there. I was going to mix some matt and satin varnish but once I had brushed off the residue and given her a wet wipe, you wouldn't even notice the difference between the door and the rest of the body, so I decided to leave it at that as you could easily overdo it. Job done, thanks to your advice, so I owe you a pint my friend.
As for everyone else on here, I thank you for your input.
To crompton 33 (a lovely loco indeed), I have railmatch paints but I no longer use enamel unless it's an emergency. I find acrylic so much more flexible and if enamel had been the problem on my Class 29, it would have been much harder to remove. Also, if the consistency of acrylic bothers you, you can easily thin it out with water, and then apply a 2nd coat if anything shows through. Watercolour etc. painting is another hobby of mine, so I am at ease with that particular medium. Most modern day artists have now ditched oils in favour of acrylic.
As for 21C1's suggestion, I won't be visiting my local Dulux centre in B&Q's as I have no intention of decorating my loco with wallpaper, no matter how original it may appear.
Once again, many thanks to everyone for their advice.
Paul.