I've seen a lot in the news over the past couple of weeks about the UK having to take part in the EU Parliamentary elections, if they still haven't left the EU by 22 May. For example:
BBC Brussel's reporter Adam Fleming says: "The EU are absolutely insistent that if the UK stays in the EU beyond 22 May then the UK has to take part in the European Parliament elections.
"They are uncompromising about that."
Why would the UK have to take part? What would happen if the UK just flatly refused to participate in the elections?