I thought that the rules regarding foreign ownership (under EU rules) was that "effective control" had to be held by EU ownership. i.e. Air france/KLM cannot buy a share and rubber stamp Delta decisions? On the face of it, of course, "effective control" is with Branson and AF/KLM but if the regulator were to see AF/KLM blindly agreeing with everything Delta wanted it would fall foul of the rules. Disabuse me!
Besides, with the uncertainty of Brexit, it appears to be somewhat of a leap in the dark. I've seen a number of decisions recently within aviation that seems to imply that airline bosses think Brexit will have minimal impact on British aviation. What do they know that we do not?