You will not get surround sound from a 2.1 system. You will get improved sound over your current TV speakers but it will not be surround.
Have you looked at the Onkyo HTX 22HD system. This is £220 for 2.1 with the option to upgrade to 5.1 if you want to in the future.
To be honest you have a very limited budget so will be hard to build anything in terms of separates. Do you have any other sources or plan on getting? i.e. PS3 or bluray player or DVD etc.