Ok, since you don't seem to be able to grasp the difference let me spell it out for you.

1. Every constructional part of an airplane needs certification before it can be used in an airplane.

2. The UK has no national internationally recognized system of certification. And will not have time to put this in place before march 29th of next year. This non existent organization can not ever start the process of accreditation for the EU before March 29th next year.

3. The EU certification for parts produced in the UK lapses at the moment the UK leaves the regulatory space of the eu. Those parts may no longer be used by airbus in their planes.

4. Airbus does not threathen to relocate its production process, airbus will be forced to relocate if it wants to build airplanes that are allowed to fly.

And by the way, similar obstacles will be faced by pharmaceuticals, automotive and chemical industries. Not to mention your airlines.