I'm a current politics undergrad at Manchester, and I'd recommend it. There's an incredible level of choice in terms of what modules you take, especially if you take the BA(Econ) route. There are also PPE and Politics & IR routes.
Hull and Aberystwyth are both known to have good politics departments, even if they are less world-renowned as universities; Hull is particularly good for anyone wishing to go into politics as a career, as they have a Westminster placement scheme. In a similar vein, Leeds' Politics & Parliamentary Studies degree (v. competitive though) involves spending your third year on placement, half in Westminster, and half in Washington DC / Ottawa. Birmingham seems to have a good department - I liked it when I visited, and they've got social policy options too, which attracted me.
Many universities offer study abroad options, even if it is not hugely obvious on the prospectus, so make sure that he does some 'digging' on the website to find out before he discounts anywhere.
Does he know if he's particularly interested in studying a particular region's politics? For instance, Exeter is a bit obsessed with the Middle East (I think that may be the case for Durham too, but double check that one), whilst Cardiff focuses on Europe.
Be aware that the UCAS entry point referred to on the league tables don't refer to requirements, they refer to how many UCAS points people go with. That can include everything from 'proper' A Levels to General Studies to A Levels in a person's native language (invariably ignored by universities) to pony care qualifications. Ignore it. If you want to check out a university's entrance requirements, then look at their website.
If it's possible, then get him to take Gov & Politics A Level - although it's not a hugely common A Level to be offered, hence universities won't demand it. Otherwise, subjects like History, Economics, Geography and English Lit are good 'fits' with Politics. Don't let him take Law A-Level - it's seen as a soft subject.
Finally, make sure that he visits the open days - I found them invaluable, less for telling me where I did want to go (although I did get a good "feeling" about Manchester, and I've been very happy here) but more where I didn't want to go - I hated the isolation and sportiness of Loughborough, and for reasons that I could quite put my finger on (although it really was just me), I really didn't like Exeter!