Soundbars are a good alternative for those who don't want a full 5.1 set-up (we rate the Yamaha ones highly), though not sure what's available for £100-150.
Just had a look on Amazon and there are soundbars in your price range from Sharp, Samsung and Phillips but I have no idea what they sound like or what you are expecting from one. I have a Panasonic 2.1 soundbar that does a perfectly good job of taking over from the TV. It is surprisingly good but that is @ £300 now.
I´ve listened to a couple and they are surprisingly competent, I´d say. I suggest you go to some store and have a go at listening to them yourself. Everything is relative, of course.