niknak, dunno why but I always had you down as younger from your posts!
As to your question, £700 should get you something very respectable. Personally - if it were for me in that situation - I'd be looking for a PC rather than Mac unless it's for a graphics/art type course simply because the range of software is greater and the uni will probably use PCs. Something in the order og a 2GHz Core 2 Duo processor will be fairly future-proof for 2-3 years, I'd go for more RAM rather than a faster processor, pretty standard these days but I'd want Ethernet and wi-fi built in, widescreen and DVD playback for chillin' out with. HDD at least 120GB, and probably bigger, 250GB is not uncommon and if son is into music, movies and the like it will soon fill up. Personally I wouldn't worry about battery life - whatever the manufacturers say is likely to be little short of fiction and in that environment there'll probably be plenty of places to plug it in - if you do go for true longer life batteries I suspect you'll pay disproportionaly for it.
I tend to buy from
www.ebuyer.co.uk - never had any problems with them and they tend to have good prices. As for brands, Acer are pretty good in my experience - reasonably priced and functional. A friend bought a Fujitsu Siemens lappie - it's going back maybe four years - seemed a bit pricey then but I think they're more competitive now - built like a tank (although not unreasonably heavy) and stylish with it.
Whatever you get, I hope son puts it to good use, passes courses with flying clours, gets good job and supports you in your dotage in the way you've always wanted to become accustomed !