"Is it not time the Iranian diplomats here are expelled"
Unfortunately this Government, and others, have far bigger issues with Iran than the execution of a single person. So it's not going to happen.
And how do you think this country would react if we were punishing a paedophile and a country where sex with 13 years olds was legal started having a go at us. We'd view them as being immoral and interfering in things that have nothing to do with them. You'd see headlines in the Mail saying that the law is the law, the offender broke it knowing what the punishment was and so on and so forth.
In a way this benefits the Iranian Government as they can now turn around to the Iranian people and say "see, those people in the west do interfere with our internal legal affairs, we told you you cannot trust them, we were right!"
All things told a very nasty affair and I can't see it ending anyway but badly.