You would also need either UK or EU to be in desperate short supply of pilots to need the foreign nationals, which there is no short supply
There is a definite short supply of good quality candidates for both seats. UK airlines are struggling to manage expansion plans and recruit at the same time and lobbying is going on to allow EU licenced people access to the UK employment market without having to jump through all the mess of converting licence. It is likely to be a one way street only as the EU is supposed to not want 'reciprocal rights' but this appeals to the companies and government in the UK as it supresses above inflationary pay rises and terms/conditions, aims to keep inflation low if possible - and also is better for the companies as keeps the bottom line and more profitable operations for them.