All sounds like good advice. Few points?

"Phil L"

No, manufacterers add the word 'bathroom' or kitchen' to paint and varnish
for one reason only, to add to it's price - I swear I saw last week in B&Q,
a tin of paint with the title 'Kitchen ceiling paint' - WTF?

So basically I can just stick with the ordinary Ronseal Quick dry stuff (20
min touch dry - I culd actually use the loo and read paper while drying).

Is it worth considering B&Q Homebrand even?

Fiddly and largely a waste of time, tape and effort, the hinges don't
matter, you can varnish over them (but don't allow runs), the handle and
keeper can be cut in easily enough.

Not sure what you mean by easily cut?

finally if I do by a better brush, what source of price should I go for.
Any other brush buying tips - I am a complete laymen, this is the first
house object I have ever painted.
I have two doors to do in total and some other MDF bits of wood (but these
will be coloured to match walls).

Thanks for your input.