Britain believes that the US could allow Ukraine to use long-range cruise missiles against targets in Russia within weeks.
Antony Blinken, the US secretary of state, and David Lammy, the foreign secretary, will travel to Kyiv on Wednesday for talks over the use of weapons, including British-made Storm Shadow missiles, in what would amount to a pivotal moment in the war between Russia and Ukraine.
The US has harboured deep reservations over granting Ukraine permission to use long-range missiles inside Russia because of fears of escalation. They are particularly concerned that Russia could respond by deploying nuclear weapons.
However, British government sources now believe that there could be a shift in the US position before a gathering of world leaders at the UN in New