You might be lucky. Some TV's have outputs for external speakers and you can just plug a couple into it. If that's all you want to do then don't bother with centre speakers, subs and all that crap. What most people fail to realise is that by far the biggest part of the improvement of going to a surround sound system is the move from the tiny speakers in the TV to decent sized ones. Most flat TV's simply don't have the room for anything else, plus they assume most people will use a surround amp, plus it's an opportunity for them to save money. Funny to think that the speakers fitted to TV's twenty years ago are better than what you get today...
Meanwhile, back at the ranch.
Buy a cheap used 'stereo' amp, any Rotel should do, and a pair of decent bookshelf speakers, anything from a major speaker company. Should get change from £100 and that will sound vastly better than the sound from the TV or any surround sound system you could get for the same money. Quality over quantity and you won't miss the channels you've never had.
You just need to check that you can get stereo out of all of the boxes, you should be able to. If you can get them to go through the TV and out one socket/pair all the better. If you buy a Rotel receiver that'll give you FM radio, which sounds much better than digital radio. How does that all apeal?