Personally Matt, I think a covert camera should be in addition to a big fuck off clearly visible camera to act as a deterrent.

The only problem with that I suppose is a decent thief will see it and think there's some special goodies in your house...

There's some good value 2/3/4 camera set ups here http://www.cctvdirect.co.uk/CCTV+Kit...+CCTV+Kits.htm

Let me know if you go for one as I'm thinking about it too and they may do a discount!