A potential doomsday deal was discussed at crunch talks between Joe Biden and Sir Keir Starmer on Friday at the White House, The Sun on Sunday can reveal.
The mullahs’ decades-long bid for the bomb is believed by some intelligence sources to be close to an endgame with the desperate Kremlin feared to be getting them over the line.
The US and UK declassified intelligence last week to reveal Russian President Vladimir Putin had taken a shipment of Fath-360 ballistic missiles from Iran’s Supreme Leader Ali Khamenei.
US Secretary of State Antony Blinken used a visit to London to warn: “Russia is sharing technology that Iran seeks — this is a two way street — including on nuclear issues, as well as some space information.”
The threat was chewed over by the PM and President who were said to have acknowledged the massive risk of the global gamechanger that Israel says would see them wiped out.
In retaliation for the missile shipment, Iran Air has been banned from flying over or landing in Britain and Russian shipping firms have been slapped with sanctions for transporting the rockets.
The White House summit discussed allowing Ukraine to use UK-made Storm Shadow missiles to strike military targets deep inside Russia — but no final decision has been announced.
Foreign Secretary David Lammy accused Tehran of a “dangerous escalation” but the Iranians denied they were involved.
Meanwhile, Boris Johnson — a close ally of President Zelensky — has spoken movingly of the plight of hero Ukrainian troops on the sharp end of Putin’s bombardment.
On a visit to Ukraine, he pressured the US and UK to allow Zelensky to use British kit to hit Russian targets.
The ex-PM told the Sun on Sunday: “It is heartbreaking to visit wounded veterans in recovery centres — as I have in Kyiv this weekend — where Ukrainian heroes are being treated for injuries they suffered in the past few months.
“And to think that some of these casualties could have been avoided if we had given Storm Shadow permissions earlier.”
He added: “There is no conceivable case for delay.
“The only person who fears escalation is Vladimir Putin and every day that goes by is a lost opportunity to save lives and bring about a just conclusion to this war.”
Sir Keir travels to Italy tomorrow where he is expected to discuss using the Storm Shadows inside Russia — as the Italians have a stake in the lethal airborne weapons system.
British sources say the PM would next be urging the French and Germans to back his support for the major escalation in Western support for Ukraine.
But Joe Biden is worried the missiles could fuel an escalation of the conflict.
Sabre-rattling Putin has warned that Russia would be “at war” with Nato powers if they signed off use of the long-range missiles.
British politicians and military experts have warned of a new axis of evil between Russia and Iran, and say this could plunge the West into World War Three.
