2 different sorts of rubbish clear coat
What you get in Halfords is cellulose. Soft, and not very solvent resistant. Singlepack (or 1K) is a bit better, but still very soft. It's acrylic, I think.
Thing is, two-pack paints and laquers contain isocyanates (I think, something like that) which are what they sound like, bad juju. Clearcoat's the hardest part to do right, and also probably the most important part, if you ask me... I'm not sure what's the best clear coat you can get in a can, I'd say 1k is better than cellulose though.