A prominent hardline Iranian cleric said expelling Britain's ambassador would be "the best thing that can happen to him" as otherwise loyal supporters of slain general Qassem Soleimani could "chop him to small pieces," the Eslahat news website reported on Tuesday.
Britain's envoy Rob Macaire was briefly detained on Saturday, a move London said was a violation of diplomatic conventions.
The ambassador said he was attending a vigil for victims of a plane disaster, and Iran accused him of attending an illegal protest.