Sorry for the delay. I'm not feeling well and I've been laying down most of the morning.
Since they say you're in the coverage area, you should be fine. 512kbps is better than 56kbps. It won't be the fastest internet in the world, but you will definitely see the difference over dial-up. If that's all you can get there and the price is reasonable, I'd go ahead. I don't know what other options you have in the UK as far as internet goes. There's satellite, but judging by Britain's usual weather, I wouldn't recommend that.