Britain would not rule out the possibility of taking military action in Iran, MPs were told during Commons exchanges on the Persian Gulf crisis.

The point was made by Ben Wallace, the Defence Secretary, who said if British citizens or armed service personnel were killed by Iranian actions, then the UK's response "would no doubt be proportionate".

MPs were debating the tensions in the Middle East following the US drone strike last week, which killed Iran’s top general Qasem Soleimani.

Sir Ed Davey, the acting Liberal Democrat leader, asked Mr Wallace: “Given how damaging the Iraq War was to security in the Middle East and given the Government's support for reducing tension, will he now rule out any British involvement in any attack on any site in Iran?"

The Secretary of State replied: “I'm not going to rule out anything. The UK will do what it has to do to defend its persons, its citizens and wherever it needs to do that; that is our duty.

"We cannot say what is in the minds of Iran or anybody else in the future and that's why we will always reserve our right to take that decision at the time of it," he insisted.

The SNP’s Tommy Sheppard asked if there were "any other members or officials of the Iranian Government whose assassination the United Kingdom would find acceptable?"

Mr Wallace replied: "I mean, I don't know how to start on that question. The United Kingdom would always seek to follow international law in dealing with threats against it."

Jeremy Corbyn accused Boris Johnson of "hiding behind his Defence Secretary" by not making the Commons statement himself.

The Labour leader asked Mr Wallace: "Could he tell us where the Prime Minister is and what is he doing that's so much more important than addressing Parliament on the assassination of Iranian general Qasem Soleimani; an extremely dangerous and aggressive act that risks starting yet another deadly war in the Middle East."

The Secretary of State replied: "This Prime Minister believes in a Cabinet Government and letting the members of the Cabinet, who are responsible for the policy to come to the House to be able to answer the questions around the policy matter."

Stewart McDonald, the SNP’s defence spokesman, asked about the US attacking Iran’s cultural sites after the prospect was raised by Donald Trump.

“Does he agree with the International Committee of the Red Cross that the threat to target cultural sites, as made by the US President, would be unlawful?”

Mr Wallace replied: “We would, of course, condemn any attacks on heritage sites and we recognise they would be against international law.

“My counterpart, Mark Esper, the US Defence Secretary, has already clearly said that the US will not target heritage sites. If anyone were to do that, no matter whether they were friend or foe, we would, of course, call them out.”

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Mr McDonald also asked if the Government had done its own legal analysis of whether the US drone strike was lawful. “I ask him simply: does he believe that the strike was lawful?”

The Defence Secretary insisted Britain backed the international rule of law, which was why it supported UN Article 51 on the inherent right of a nation to defend itself.

“How a nation takes those sometimes very difficult decisions is, first, a matter for that nation and the intelligence and evidence it has in front of it at the time.”

He added: “What I can say of the intelligence I have seen is that there is definitely a case to answer on the cause of self-defence.”