The government control over the mainstream broadcast media is exerted by the simplest of means. Money.
Over 300 pigs at the BBC earn more than £100,000 each and the backbone-free waste of skin Mark Thompson gets an eye watering £817,000. Naturally, they would not wish to lose their trough, so the threat of reducing or removing the licence fee is sufficient to compell the piggies to toe the government line. They'd find it harder to enjoy the same level of pay and privilege in a purely commercial environment.
On the other side of the fence the commercial channels are terrified of havingto share their advertising revenues with the big beast that is the BBC, and so they offer fuck all resistance to the governmnet line either.
That is why you have to go outside of these corrupt and fearful purveyors of propaganda dressed up as news if you want to know what is happening rather than what the government want to tell you is happening.