I'm in Lincolnshire and manage to grow most stuff. It does take a little more attention (I'm useless during the early months of the year because I always forget to check for frost warnings...).
This year has been dismal so far :S because of the cruddy weather.
In fact, in the UK to a certain extent it's not so much how far North you are, but how far East. I have a friend about "level" with me but on the West of the country and he struggles with his garden. We tend to avoid a lot of the worst weather over here ;D
Growing in London is damn easy, especially if you get a mini green house from Wilko to extend the growing season earlier and later in the year.
In the North it really depends on your garden. I have friends in Sheffield with protected terrace house gardens, who grow nearly as easily as me, but my folks with a mildly exposed small holding have a chore getting them providing as many tomatoes as I do - but they won't get a green house.
I had to tie mine to my garden fence to stop it toppling over. They never seem to last more than 3 or so years - but for £12 I don't mind too much - just a shame you can't just replace the plastic.
You think it's bad in the UK? I'm actually missing the variety you can find in supermarkets in the UK compared to the water vessels they sell in South Africa. At least sometimes I could strike it lucky with a Tesco finest from the Isle Wight on a good year.
