Can regulators stop the march of media consolidation?

One of the most important regulators in Britain, the Competition and Markets Authority, has ruled that 21st Century Fox's proposed takeover of Sky would not be in the public interest as it would give one organisation (and the Murdoch family behind it) too much control over news in the UK.

Of course, there are lots of questions behind such a ruling.  For example, what is the 'in the public interest' and who decides on what that is?  There has also been the suggestion that the Murdoch family would possibly shut down Sky News in order to satisfy the regulator. However, would that just end up reducing the number of different perspectives in the UK news landscape?  Lurking behind all of this is the question of what happens if Disney's proposed takeover of 21st Century Fox itself takes place?

There are lots of articles online about this issue but this one from the BBC is a good place to get started.