The one place I can find that has what you're looking for is Richer Sounds:
Richer Sounds - The UK's Hi-Fi, Home Cinema & Flat Panel Tv Specialists!
You can pick up a Sony or Yamaha (I'd personally advise the Yamaha) amp for around a hundred quid and a set of Yamaha NSP110 speakers for around £80. BUT: by the looks of it, you'll have to drive to the nearest store to pick up the amp; I don't think they are doing them by mail order (but it will do you no harm to pick up the phone and ask - I've always found Richer Sounds to be very friendly; and no, I don't have shares in the company).
The sound you get from this system should be pretty good.
Be warned that home cinema amps tend to be quite large and can run quite hot - you will need decent ventilation around and above them.
You will also need speaker wire (get the cheapest that's necessary for the job - trust me, there's zilch difference). You will also need 2 optical interconnect cables (if not already supplied) to link to the amp. Richer Sounds has basic cables etc, or you could try ebay if you have an account.
The two amps I've mentioned have two optical inputs (but check the specs of each amp carefully - some in this price range only have one). That means you could connect the Sky and the PS3 to the amp. This would leave your TV unconnected, but do you really need it? Bear in mind that if you are watching a Sky programme, the sound is being fed through to the amp anyway - you don't need the TV linked up as well.
Plus, a little tip - I'd have a sound connection to the TV from Sky as well. It's a bit of a pain to switch on the amp just to listen to the news or the shopping channel and late at night, the sound from an amp can be a bit annoying if the rest of the household has gone to bed. Just remember to turn the sound down on the TV when you start watching through the amp, or you'll get a weird echo.
Two other things:
(1) as soon as you can, get hold of speaker stands (Argos sell some perfectly okay ones for about 20 quid) for the speakers if otherwise they're sitting on the floor, stuffed behind the sofa, etc. You'll find this improves the sound a great deal.
(2) you should ideally get something like Digital Video Essentials' (a DVD) that gives you various visual and sound 'tests' to help calibrate your system properly. I know it sounds very geeky, but I promise you, it's ten pounds well spent.
You then have a separate set of speakers, amp and DVD player. Now if in the future you want to upgrade or replace anything, each part of the system can be treated separately - this makes things rather cheaper in the long run.
One other thing - probably you already know this, but some home theatre amps are 'receivers' others are plain 'amps'. The only difference is that the receivers have an inbuilt radio (typically just FM, not DAB) - get yourself a suitable aerial and you have a decent radio as well (though it's a bit redundant given that Sky offers so many radio channels and in digital quality sound).
Hope this helps and don't hesitate to ask more questions!
