Well, after wading through the whole thread and reading what people said, I had to try this ...
So off I went to B&Q's website and carefully examined the range of glues available.
I plumped for this one:
Decorator's PVA. Checking the Material Safety Data Sheet confirmed it was nothing other than a mix of polyvinyl acetate and polyvinyl alcohol.
(What can other UK users recommend from experience...?)
The test vinyl chosen first was a very old, scratched and beaten up copy of Patti Smith's 'Horses'... if I made it worse, it was already pretty badly nicked and scratched ... if I made it better, it was a bonus
Made a complete mess of first coat of first side, including getting some on the label. But remember! it's water soluble ... so a wet bit of kitchen towel solved that. Left it to dry for a while, flipped over, did second side (did a better job that time ... putting a chamfered edge on your spreader helps a lot...!). Went shopping and came back. First side still wasn't dry (I did say I'd made a mess didn't I? Bits of it were far too thick...). Eventually it dried and I peeled it off.
The difference? Well it made a fair difference, but didn't do anything about the scratches of course. The whole record does sound a lot nicer and clearer though ... especially the quiet bits of 'Horses'.
It wasn't a good test candidate like I said, so I'm doing a rerun now with a 'clean' unscratched record ... side 1 of The Orb's Live 93. Several attempts at washing have all failed to get this cleaned completely, so we'll see what happens ...
Incidentally the B&Q glue peels off quite nicely and doesn't seem to leave much static charge, unlike some have reported.