Iran has arrested Rob Macaire the UK ambassador to Iran for a brief period for participating in the Tehran protests for shooting down the Ukraine plane. He joined a group of people in front of Amirkabir University in Tehran on Jan 11, 2020 and was arrested half an hour later.

The ambassador Rob Macaire has denied this claim and said he went to the event which was advertised as the vigil for the victims of PS752 tragedy in which 176 people are killed. He confirmed on twitter that he just left the place after 5 minutes after some people started chanting slogans.
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— Rob Macaire (@HMATehran) January 12, 2020
Detained half an hour after leaving the area. Arresting diplomats is of course illegal, in all countries. See comments by Foreign Secretary @DominicRaab. https://t.co/djpr99iSwI
However this did not go well with the Iranian authorities and arrested the UK ambassador Macaire at a barber shop when he stopped on the way to the UK embassy. He was held for three hours and summoned on Sunday for more explanations.
♦️#سفير_انگليس در تهران به دليل تحريك و ساماندهي تحركات مشكوك در مقابل دانشگاه اميركبير براي ساعتی بازداشت و سپس آزاد شد/تسنیم pic.twitter.com/zBKx8wDgA0
— 🌐 اعتمادآنلاين (@EtemadOnline) January 11, 2020
Iran media and government accuses him of provoking the anti government protests.
Meanwhile UK Foreign Secretary Dominic Raab and other leaders and officials condemned the incident and said its violation of the 1961 Vienna Convention.