The UK has demanded an apology from Iran’s ambassador in London after the arrest of Britain’s top diplomat in Tehran.

Rob Macaire was detained as demonstrations broke out over the downing of a Ukrainian airliner by Iranian forces and was subsequently called in by the foreign ministry in Tehran to explain his “illegal and inappropriate” presence at the event.

Foreign Secretary Dominic Raab said it was a “flagrant violation of international law”.

Iranian ambassador to the UK Hamid Baeidinejad was being summoned to the Foreign Office “to demand an apology and to seek full assurances that this will not happen again”.

Mr Raab said that “given the treatment of the ambassador” security measures at the embassy in Tehran were being kept under review.

Middle East crisis
Hamid Baeidinejad, Iranian ambassador to the UK, leaves the Foreign and Commonwealth office (Jonathan Brady/PA)

He told MPs that Iran now faced a choice about its future direction.

“The regime in Tehran is at a crossroads,” Mr Raab said.

“It can slip further and further into political and economic isolation.

“But there is an alternative and the regime does have a choice: the diplomatic door remains open, now is the time for Iran to engage in diplomacy and chart a peaceful way forwards.”

Footage has been published by Iran’s semi-official Tasnim news agency which appears to show Mr Macaire at what it calls an “illegal gathering”.

Defending himself, Mr Macaire said that he went to an “event advertised as a vigil for victims” of the Ukraine International Airlines PS752 tragedy on Saturday to pay his respects to the four dead Britons but “left after five mins when some started chanting”.

Mr Raab told MPs: “He was not attending or recording a political protest or demonstration.

“His arrest later that day without grounds or explanation is a flagrant violation of international law.”

AIR Ukraine
(PA Graphics)

Iran’s Revolutionary Guard admitted accidentally shooting down the Ukrainian jet with the loss of all 176 people on board, including four Britons.

Families of the victims could seek compensation from the Iranian government, Downing Street indicated.

The Prime Minister’s official spokesman said: “As a first step we need a comprehensive, transparent and independent investigation to know exactly what happened.

“Of course the families of the four British victims deserve justice and closure and we will continue to do everything we can to support them in getting that, including options for compensation.”