Generally TV's dont include 5.1 decoders. The easiest way for surround movies, would be to connect a DVD player with integrated 5.1 decoders.. easy to tell, it will have a lot more audio outputs on the back.
Unfortunatly many DVD players output their audio as a digital stream instead. But players with integrated decoders still exist.
You dont actually mention if this is a powered speaker system. If its just 5 speakers, and a sub, then you would need an AV Amplifier, and of course you still need a surround sound source (like a dvd player).
Most TV isnt broadcast in 5.1, nothing on freeview, or terrestrial analog supports it. Sky does broadcast 5.1 on Sky Movies, and I believe the Sky HD channels also include a 5.1 audiostream, but you need an AV Amp or Processor to use it. The skybox only sends a stereo feed to the TV.