Foreign Secretary David Lammy has urged Iran to take “the off-ramp” and return to the negotiating table.
Iran has vowed there will be “everlasting consequences” following US strikes at the weekend, intended to take out the country’s nuclear programme.
Lammy said he had told Iran that it would be a “catastrophic mistake” for them to retaliate by firing at US bases, or by blockading the key shipping lane of the Strait of Hormuz.
Speaking to BBC Radio 4’s Today programme, Lammy said he had told the Iranian foreign minister to take a message to the Iranian leadership to “get serious about their nuclear programme”.
He added: “They have to get serious about the off-ramp that is being made available to them.
“There is still an off-ramp and I was discussing that with the Iranian foreign minister again on the phone yesterday.
“We, alongside all of our partners in the G7, across Europe and across the Arab world and the Levant, are urging the Iranians to get serious both with the E3 – us, Germany and France – but also with the United States.”
On Sunday, Prime Minister Sir Keir Starmer stressed the UK was not involved in the US strikes on three nuclear facilities in Iran – Natanz, Isfahan and Fordo – on Saturday night.
He also warned of the risk of escalation, and said he wanted to reassure people that “we’re doing everything we can to stabilise the situation”.
Pressed on whether the US strikes were legal, Lammy responded: “I don’t say it’s not legitimate” and said there was “no moral equivalence” with the UK’s clear stance that Russia’s invasion of Ukraine was illegal.
However, he also acknowledged that diplomatic efforts had not stopped the Iranians enriching uranium, so “clearly it was not working”.
The foreign secretary said the International Atomic Energy Agency (IAEA) had “confirmed the 60% enrichment” and the Iranians were still “obfuscating and engaged in deception”.
Lammy said that, if Iran obtained nuclear weapons, there was likely to be “nuclear proliferation across the Middle East, the world would be seriously more dangerous, and that’s why it must be stopped”.
He said: “Yes they can have a civil nuclear capability that’s properly monitored, that involves outsiders, but they cannot continue to enrich to 60%… Why do they need 60% enrichment if not for a nuclear weapon?”
But the foreign secretary said that “ultimately” the only solution to dealing with the Iranian nuclear programme was through diplomacy, “because the expertise still exists in the country, it’s likely that some of the material still exists in the country”.
James Cartlidge, shadow defence secretary, said the Conservatives backed the US military operation.
“The key message is to show support for Israel and the United States,” he told BBC Breakfast.
“We feel above all else that we can’t have a situation where Iran has nuclear weapons.”
Asked if the UK would get involved in the conflict, he said it was “too early to speculate” but welcomed UK defence secretary John Healey’s earlier decision to move planes and military assets to the Middle East, putting them in a position to “respond if needed”.