// Later on Sunday, deputy foreign minister of Iran Seyed Abbas Araghchi responded, also on Twitter.
He said: "He wasn't detained, but arrested as unknown foreigner in an illegal gathering. When police informed me a man's arrested who claims to be UK Ambassador. I said IMPOSSIBLE! Only after my phone conversation with him I identified, out of big surprise, that it's him. 15 min later he was free." //
So he was at an anti-Government protest, and identified as a suspicious foreigner and detained. He told police he was the UK Ambassador and they checked with their Foreign Office, and he was quickly released. Not much of a story, and it was all cleared upviaTwitter.