Senior military figures reportedly believe Iran now possesses the theoretical capability to strike Britain — but insist they are confident in NATO defences to protect the nation.

The question has been thrown into sharp focus after Israel claimed Tehran fired two ballistic missiles at the joint UK-US installation on Diego Garcia, a remote atoll in the Indian Ocean sitting 3,800km from Iranian territory. The first Iranian rocket was brought down — reportedly by a missile launched from an American warship — sometime between Thursday night and Friday. The second exhausted its fuel after covering 1,990 miles, dropping into the ocean roughly 400 miles short of the island, where approximately 100 British service personnel are based.

The Express reported on Sunday how Israel’s chief of staff, Eyal Zamir, used the episode to drive home a broader point about the reach of Iran’s weapons.

“Their range reaches European capitals — Berlin, Paris and Rome are all within direct threat range,” he said.

The Khorramshahr question

Analysts have identified the Khorramshahr-4 as the most probable weapon used in the Diego Garcia attack, reports the Times. According to Iran’s own declared specifications, the missile carries a maximum range of 2,000km when fitted with its standard 1.5 tonne warhead — a payload heavy enough to flatten a target on impact, released from the main body during the terminal phase of flight for maximum precision.

The picture changes significantly when the warhead weight is reduced. Dr Sidharth Kaushal, a senior research fellow at the Royal United Services Institute, informed the Times of the numbers: strip the payload back to somewhere between 450kg and 550kg and the effective range stretches to approximately 4,000km. From a launch site in northeast Iran, that would bring portions of the United Kingdom within theoretical striking distance. Even at that reduced weight, the warhead would retain enough destructive force to bring down a building.

The geography is instructive. RAF Fairford in Gloucestershire — currently serving as the forward operating base from which US bombers are conducting strikes against Iran — lies roughly 4,350km from Tehran.

A separate thread of concern runs through Iran’s civilian space programme. The Qaem-105 rocket has for years been assessed by analysts as almost certainly designed with a secondary military application in mind, even though no confirmed evidence of it being deployed as a ballistic missile has entered the public domain.

Why a strike on Britain remains unlikely

For all the theoretical reach, military sources speaking with the Times are emphatic that any Iranian missile aimed at Britain would face an extremely hostile passage. One source described a successful hit on London as “very unlikely”, explaining: “It would have to fly a long way over multiple air defence networks and be very precise.”

The Royal Navy’s six Type-45 destroyers provide a degree of protection but are limited to intercepting medium-range ballistic missiles — they were not built to handle weapons travelling intercontinental distances of the kind Iran would need to deploy. Britain’s primary protection against that class of threat comes from membership of Nato’s Ballistic Missile Defence system.

Matthew Savill, director of military sciences at Rusi, stated in the report: “If launched towards the UK, this is what Nato’s BMD is designed for. The UK isn’t actually defenceless against a threat launched from Iran.”

The shield in detail

The BMD architecture rests on several interlocking components. Two Aegis Ashore batteries anchor the system on the European continent — the first positioned in northern Poland, oriented towards the continent and the Baltic Sea, and capable of engaging short to intermediate-range ballistic missiles; the second at Deveselu in southern Romania. Each site is staffed by around 200 military personnel.

Four US Navy Arleigh Burke-class destroyers — more capable air defence platforms than their Royal Navy equivalents — operate out of Rota in Spain as a mobile component of the shield. An early warning radar installation at Kurecik in southeastern Turkey provides the detection layer that feeds targeting data to the rest of the network. Certain fighter aircraft can also engage ballistic missiles, though only during the initial boost phase immediately after launch.

The expert verdict

Dr Kaushal reportedly explained why the theoretical threat remains limited in practical terms.

“A missile fired over 4,000km likely has a pretty high circular error probable, which means you would need quite a few to strike anything specific. The lighter payload also means that one would be trading impact for range.

“So even though it is theoretically possible [to hit Britain], this would be a case of firing a limited capability over a well-defended trajectory with a small and inaccurate payload.”