British ambassador to Iran Robert Macaire has left Iran in accordance with the terms and conditions on Wednesday.
The Foreign Office said the trip was planned a long time ago and was "very much business as usual", according to SKY News.
It said he would be going back to Iran "in the coming days" after having a number of meetings.
Macaire took part in a protest in front of Amir Kabir University in downtown Tehran on Saturday and was shortly detained.
He was summoned to the Iranian Foreign Ministry on Sunday for “unconventional behavior” inconsistent with his diplomatic status and being present in an “illegal gathering”.
He was reminded that the presence of foreign ambassadors in unlawful gatherings is not in line with their responsibilities as a political representative of their country and it is contrary to the Vienna Convention on Diplomatic Relations of 1961.
MNA/PR