Before you lay down 200 quid on a new amp/combo you need to know what you're wanting to do first. Sounds like you're on your way to playing with others and playing small venue shows? Right? Where do you see your playing in the next 2 to 3 years?
The only reason I say this is because if you're going to limit your budget for something like this, you need to get the most out of every pound for what you plan on using it for.
If your goal is to play small room gigs, or just jam with friends in the garage, then a combo amp with 150W should be plenty.
Wanting to buy a separate amp head and speaker cabinets isn't really necessary, in my opinion, unless you're playing large venue shows and want to use your cab to hear yourself play.
It's been my experience that you can get away with plugging in to a PA system with some effect pedals and keep things “light” for you. If you're playing with a band that doesn't have a good PA system and you need to have your own set up, anything larger than 300W may not be needed. Unless your guitarist is a douchebag and drowns everyone out with his Marshal stack.
I've heard mixed reviews on Behringer products. They're on the lower price point, but the old adage of “you get what you pay for” seems to ring true with Behringer.
Ampeg makes a nice combo amp
http://www.sweetwater.com/store/detail/BA115v2. I'm not a fan of 15-inch speakers, but I've heard great things about this amp.
