Theresa May will chair a meeting of the Government’s emergency committee Cobra on Monday after Iran seized a British-flagged oil tanker in the Persian Gulf.
The Prime Minister is expected to receive updates from ministers and officials on the situation and will discuss the maintenance of the security of shipping in the region.
Mrs May was not present at ministerial Cobra meetings over the weekend – which she spent in her Maidenhead constituency – but was kept informed of developments.
Foreign Secretary Jeremy Hunt will update the Commons on the situation on Monday afternoon, amid reports that ministers are considering freezing Iranian regime assets.
He is expected to tell MPs what further measures the Government will take.
It came as ministers denied reports that the UK had taken its “eye off the ball” because of domestic politics after the vessel was commandeered in Omani waters in the economically significant Strait of Hormuz.
Chancellor Philip Hammond insisted the Government had been “very much engaged with both the Americans and our European partners in the response to Iran’s increasing defiance of the JCPOA over the last few months”.
And Defence Minister Tobias Ellwood said the UK had vessels going through 100 nautical miles of waterway every day in the region, adding: “It is impossible simply to escort each individual vessel.”
He also called for more money to be invested in the Royal Navy if Britain wants to continue to play a role on the international stage.
Meanwhile, audio footage emerged between Iranian authorities and HMS Montrose moments before the Stena Impero was seized.
In the radio recording, the Iranian vessel can be heard saying: “If you obey, you will be safe. Alter your course immediately. I want to inspect the ship for security reasons.”
HMS Montrose replied: “You must not impair, impede, obstruct or hamper the passage of the Stena Impero. Please confirm that you are not intending to violate international law by attempting to board.”
Reports from Tehran state those on board the Stena Impero are safe and well.
Iran has directly linked the seizure of the vessel with Britain’s role in detaining a tanker carrying Iranian oil earlier this month.
A spokesman for Iran’s Guardian Council was quoted as saying “the rule of reciprocal action is well known in international law” and that Tehran made the right decision in the face of an “illegitimate economic war and seizure of oil tankers”.
The explanation, which contrasts with a suggestion on Friday night that the Stena Impero was “violating international maritime rules” and had collided with a fishing boat, came as the UK Government warned British ships to stay away from the Strait of Hormuz.
HMS Montrose, which is patrolling the Persian Gulf to protect shipping, and earlier this month intercepted Iranian patrol boats surrounding another UK-flagged tanker, reportedly arrived minutes too late to prevent the latest incident.
A second oil tanker, the Liberian-flagged Mesdar, which is managed by Norbulk Shipping UK, veered off course towards the Iranian coast after it was boarded by armed guards at about 5.30pm on Friday.
Communication with the ship was later re-established and the crew were unharmed. The tanker was reportedly allowed to resume navigation.
France and Germany joined condemnation of Iran’s actions, which have triggered concerns that it will lead to further oil price hikes amid heightened tensions in the Gulf involving Iran, the US and UK.