If and when the British rejoin it will be under the EU terms Including the adoption of the Euro and full financial integration.
Expect lots of pig like squealing from the loony right then.
Not sure what the point of rallying outside European Parliament, nothing the EU can do for them. Shouldn’t they spend their time rallying in the UK? That’s where the application to start accession negotiations needs to come from.
Britain is highly welcome to join the continent. Maybe it is worth considering a new, deeply integrated entity like a European Republic.
The founding members of the ECSC/Montanunion should consider a really bold move. Britain could become its initiator and the most relevant contributor.