This is an official Canon website, so I’m sure they’ll be by shortly to give you the canned legal statement that rain may damage your camera, it's not weather sealed, blah, blah, blah. So ignore everything I’m going to tell you, because I disagree with most all of that.
I’ll tell you from personal experience that I spent a year stomping around tropical countries in Southeast Asia with my 400D. I was caught in the middle of rainstorms multiple times (though I was usually able to shove my camera in a waterproof stuff sack), and the humidity at times was practically the equivalent of rain. My camera is still clicking away happily. I’d use common sense, and I think you’ll be fine. I know GB doesn’t have great weather, but it’s hardly a tropical rainforest. Oh, and I highly recommend using a protective filter on your lenses (aka UV filters).
But, if you want to be extra safe, without spending a fortune on a shell, they make cheap plastic bags roughly fit for dSLRs that you can use if you’re going to be out shooting in inclement weather for a long time. Here’s one, but there are many types:
http://www.amazon.com/NEEWER-Camera-Protector-Cover-Rainproof/dp/B004GTIYVS/ref=sr_1_3?s=electronics...
