Britons may choose to change their minds but this is not a single party decision. The EU will likely not readmit them on the same terms and the UK is not nearly as powerful or relevant to European interests as it once was.
As a safe far away island, the UK has much more use in a captive alliance to defend a threatened continent than it is as a participant in Europe that gets special exemptions.
As a safe far away island, the UK has much more use in a captive alliance to defend a threatened continent than it is as a participant in Europe that gets special exemptions.