There is still something very funny about this insistence that the questioning happens in Sweden. Swedish police can come to UK to question. UK police could question on behalf of Swedish police, there are arrangements for that I think.
Extradition when there are no charges is unusual.
The UK have been here before, General Pinochet and the Spanish judges spring to mind.
Edit: further reading on European arrest warrants makes me realise that each country in Europe has a different definition of 'arrest'.