This is the right time to buy as lots of shops will be selling off last years bikes either right now or very soon.
After years of riding an aluminium hardtail I've just bought a steel framed one. I have found it very comfortable, not only because if the ride characteristics but also the geometry. I bought a Genesis Altitude 00 which you should be able to get for £500 or less quite easily.
If you want an aluminium bike the choice is massive, but don't buy mail order. You must try the bike before you buy it and better still, try a few. I think the Specialized Rockhopper is a sound buy but I knew I didn't want one within thirty seconds of getting on it. No one can tell you what will feel right to you.
Is it is you want to do on the bike? Where abouts in Scotland are you?