Dirk Gently The problem comes that when they have a monopoly there is nothing whatsoever to stop them putting prices up to a point where not even you would be able to afford them.

Can you please stop posting your idealistic rubbish and post from a business perspective?
They is no way in hell, even if Sky had a monopoly, that they would go even as far as double the current prices.
If they were to put prices up to a point where I'd cancel (prob around £70 a month tops for package with sport) then I'd imaging that a good 70-80% of their customers would also cancel meaning they would MAKE LESS MONEY.
Sky know the limits to which they can charge and will charge those prices accordingly - although admittidly with Virgin etc out of the way that point maybe a few quid higher than it is currently.