Imho a merger of TUI AND TCX flying operations would easily pass the regulatory agencies in the UK . Caveat the issues would likely be more about remaining high street shops - Here there would be issues to contend with due to dominance in that ever declining market place .
These companies are far from monopolies and there are mountain ranges of competition out there today, however much now resides in the ethereal domain of the internet, the consolidators and those flexible fares operators peddling “custom” built packages; Some even offering taxi or car hire transfers ( at less than competitive rates when looked at in more detail !)
Still it gives the millennials something to do calculating true cost viz value quotient I suppose !
That being said Thomas Cook looks to be getting some finance and bonds elsewhere right now.