I used to subscribe to the London Review of Books which is genuinely intelligent, and I still get Interzone (British SF magazine) when I can find it. But really, I only ever read magazines on long train or plane journeys now. There really isn't a UK magazine I can say I really enjoy completely. Outside (USA) is pretty good and I like The Walrus, which is Canadian radical current affairs mag.
All the music magazines are dull. So I read New Scientist occasionally but half the articles are really badly written and by people who apparently don't know much about what they are supposed to be explaining. Wired is still hilariously naive at times, but has some moderately good things in it. And Fortean Times, although sometimes it's just stupid these days and trying too hard to get a more mainstream audience. I used to read Prospect, but it's gone oddly smug and conservative recently.The Ecologist also used to be more intelligent but now it ditched all its progressive politics when Zac Goldsmith took over.
Then there's all these new 'mature, intelligent' (and very heavy and expensive) magazines like Intelligent Life and Monocle, but they are basically for poseur international businessmen who like to think they are part of some world-defining zeitgeist instead of just making themselves rich at the expense of everyone else.