OldLurker, Your consideration seems to strengthen my point.
You are right that being disallowed overflight of the UK would be a major inconvenience for continental EU operators. However, the UK airlines would not be better off, were the EU to play "tit for tat" here and forbid UK companies from crossing EU airspace, would they? Then it will be either the northern route around Norway or the southern one around Portugal and Spain, should an UK aircraft wish to fly to or from Asia.
While this split is most regrettable in my eyes, it ought to be executed in a civilized manner with Gentlemen on both sides of the table. No need to wheel out perceived strenghts that may well turn into weaknesses upon closer examination. From both sides.