So basically extradition laws state that if courts of some random country feel that British citizen violated their laws and they claim that this happened on their territory although this citizen never actually was there, he can be expelled from UK to be judged there if British judges believe that he will get fair trial there, whatever the laws there might be?
So Iran could put some "secret" documents up on the web. SEO it, grab credentials of all British citizens accessing the site and demand their extradition?