The UK is currently in a transition phase on terrestrial TV from anologue to digital. TV is regionalised and the digital channels(Freeview) are currently being run in parallel with the analogue 5 basic chanels. Over the course of the next couple of years region by region the analogue transmitters will be turned off. After that date if you don't have a Freeview box or a tv with built in Freeview or don't subscribe to Sky or Virgin, you won't get any channels at all, there is another problem however. The legacy analogue regional TV system is based on each region using a different part of the frequency spectrum, this allows Tyne Tees for example to broadcast local news and programmes to the North East, whilst allowing adjacent Yorkshire to do the same with local programming in its area, to this effect each region uses one of three frequency specific aerials. Allthough all these different aerials will get some of the Freeview channels, none will get them all. So if you move into a house thats not had Freeview before, then you will probably need to change the aerial to a wideband type to get all the Freeview channels, otherwise you will get some, and the rest will pixalate, freeze and generally be a pain.
There are two other options, cable and satellite. Sky is the satellite broadcaster in the UK and provides the platform for most of the other satellite subscription channels. There are numerous packages but generally if you want the standard entertainment channels, lifestyle, discovery, childrens etc it is about £20 per month, the sports channels and the movies are both classed as seperate premium subscriptions with one of them taking the cost upto about £35, and both taking it upto about £50 per month. All of the large urban centres and most smaller towns are fully cabled with optical fibre and offer a service run by Virgin Media. Most of the channels are the same as you will find on the Sky system, but because most of them are licensed off Sky their packages are normally slightly higher than Sky, and don't usually offer as many channels in total, because of the bandwidth limitations of the optical fibre network infrastructure, both systems of course have all the Freeview channesl as well. Both Virgin Media and Sky usually give you the Digital HD Box free of charge, and both normally fit the system free of charge or for a small nominal charge.