Hi Anthony,
What I would do is to browse the local bike shops looking at new bikes in the £400 / £500 price range and have a sit on them to see what fits.
( Make a note of models, prices & sizes for reference later. )
This won't be a waste of time for you or the bike shops as sooner or later you will buy one anyway. (Trust me. I did)
Go home and search
eBay & Gumtree for second hand versions of the ones that took you fancy in the shops and be patient and don't buy
the first thing that comes along.
If you buy wisely then you'll be able to re-sell without loss when the bug has bitten and you buy a better one.
Cheers,
Paul G