The UK can sell security
Please elaborate, because the last “security” thing I saw out of the UK was their stupid bill attempting to back door encryption as well as having vendors sit on zero days so they (and hackers out there) could exploit them. None of that would be good for the EU, let alone the world.
The whole point of the EU is to stop Europe from continuously going to war with each other.
The UK has a very credible military base. Germany and France have tried in the past to combine the military forces of Europe. This is not to undermine the French who also have a credible force. Germany does not and could not argue it was in the same league. The UK military has been diminished under the Tory government, but the expertise is still around.