Storm Shadow missiles, and their French equivalent called SCALP, have been sent in limited quantities – low hundreds not thousands – to Ukraine and so far have only been used against targets inside its borders.
Ukraine has already used them against Russian-occupied Crimea – for example hitting Russia’s Black Sea naval headquarters at Sevastopol.
These missiles, which are launched from an aircraft, fly close to the speed of sound and carry highly explosive warheads making them an ideal weapon for penetrating Russian bunkers and ammunition stores.
Protracted discussions about firing Storm Shadow missiles deep into Russia were raised during July’s Nato summit in Washington.
Starmer insisted the missiles were to be used for defensive purposes but said “it’s up to Ukraine to decided how to deploy it”.
In a message on X at the time Zelensky wrote he had “learned about the permission to use Storm Shadow missiles against military targets in Russian territory”, adding that he and Starmer had the “opportunity to discuss the practical implementation of this decision”.
But nothing actually happened after the summit.
Zelensky made it clear the use of long-range missiles are a key part of his “Victory Plan”.
He raised the issue again when he went to Downing Street to brief Starmer last month, in a meeting attended by the new Nato secretary general Mark Rutte.
There was no change in policy, but Rutte said there was no legal reason to prevent Ukraine from striking Russia if the countries who supplied the missiles consented.
UK Defence Secretary John Healey has worked hard to avoid to show any public disagreement with Washington. When recently asked about the matter in a joint press conference with US Defence Secretary Lloyd Austin, Healey said such discussions in public would only help Russia.
The fear is that although Russian President Vladimir Putin’s threats have turned out to be largely bluffs, allowing Ukraine to hit targets deep inside Russia with Western-supplied missiles could provoke a major escalation.
Kremlin spokesman Dmitry Peskov warned Putin had expressed such a move would put Nato “at war” with Russia – as such strikes would ultimately be carried out not by Ukraine but by the countries that give permission for such use of missiles.
Professor Justin Bronk from defence think tank the Royal United Services Institute told BBC News it is “very likely” that US President Joe Biden’s belated decision to allow long-range strikes with ATACMS ballistic missiles will also enable Storm Shadow to be used in at least the same way.
“US objections will presumably have been dropped for them,” he said.
“Russian threats are unlikely to be considered a significant deterrent at this stage, since Russia has threatened dire consequences – including allusions to nuclear attacks – repeatedly throughout the war at each stage when Western equipment has been supplied.”
But he said there is little reason to think that expanding the usable area for UK Storm Shadow “will make any difference” to Ukraine’s ability to hit back at Russia.
He added “most of the more critical targets such as fighter bombers on Russian air bases are likely beyond the range of these missiles in practical terms – and there will be a limited number of the missiles available after lengthy combat use of the system in the war to date.”