Washington, in particular, fears escalation. Even as Mr Biden was due to allow Storm Shadow strikes inside Russia, he was reportedly resisting pressure to allow the US equivalent missile, the Atacms, to be used for the same purpose.
It is not the first time that Britain has led the way in terms of driving through the donation of new weapons to Kyiv.
It took Ben Wallace, former defence secretary, to agree to sending Challenger 2 tanks before Washington agreed to sending its own Abrams war machines to Kyiv.
Sources also claimed Mr Wallace’s hopes of becoming Nato secretary general were scuppered by the White House because he moved without US permission to announce Storm Shadow and F-16 donations to Ukraine.
The Biden administration eventually agreed on each of those capability donations, but not after expressing fears they could trigger an escalation of the conflict beyond Ukraine’s borders.
A Western official told The Telegraph that threats from the Kremlin about the prospect of a war between Russia and Nato are overstated.
That is because European governments mostly feel that Putin himself believes he is already engaged in a major conflict, perhaps on the same scale as those fought between 1914 and 1945.
One source said the Russian president is not interested in escalating the conflict upwards towards a nuclear war but has visions of what was described as a “horizontal escalation”.
This includes hybrid attacks, such as hiring agents to burn down commercial properties linked to Ukrainian support or attacking railway infrastructure carrying military aid east to Kyiv.
“It’s not just nuclear escalation we have to be mindful of,” one official told The Telegraph.
“This is Putin’s way of bringing the war to the West, much like Ukraine has done so by invading [the Russian region of] Kursk.”
Analysts have noticed that Putin’s red lines are often crossed – and without much in the way of retaliation.
In his address to announce the start of his “special military operation”, the Russian president said there would be “consequences greater than you have faced in history” if the West joined the war.