I'm intrigued. Given that over the past few years UK nationals working in EASA and the various other European agencies will, like me, have been acquiring some form of European citizenship (and EASA is in Germany, which allows dual UK-German citizenship if applied for before the end of the transition period), how many Brits will be willing to move back? Their jobs are secure, and if they've been working in Cologne since the beginning, as implied by Mr. Shapps, their lives must be pretty stable? Move back to regulate what little manufacturing is left?
I work in automotive at the moment, and have acquired a second European passport to maintain my position here. It would take quite the package to persuade me back right now.
I doubt that the UK has any right of recall over these people - they aren't diplomats - and so will have to be tempted back. What would tempt you back? Assuming, that is, that you aren't one of the jingoistic sorts on here who would never have gone in the first place...