The BBC has suffered well-publicised cutbacks and can't afford to buy in many 'big budget' movies.
The independent channels are all struggling to survive. ITV1 in particular has come close to closing down several times over the past year or two. (It's lost 80% of its advertising revenue).
There is only a finite amount of advertising revenue which, through the advent of digital TV, is now spread across a greater number of channels. Further, advertisers are now switching the majority of their output to online media (particularly to social networking sites). All of this has come about at the same time as an economic downturn, which has seen companies cutting back on their advertising budgets.
You can expect to see several commercial channels disappearing within the next year or two. Those which are jointly owned by the BBC (such as the UKTV group, including Dave, Yesterday, Really and GOLD) will probably survive but some of the ITV group, including ITV1, might well go under. If so the programmes which attract lots of advertising (such as Coronation Street) will survive, but they'll move to Sky.
Chris