“Zelensky is also having to deal with the growing unpopularity of the war among the population and the discontent among troops, with desertions growing rapidly.

“We desperately need peace negotiations but, just as in Tony Blair’s time, our government, given a choice between international law, morality and common decency, will always come down on the side of war.

“Starmer, Lammy and the rest must be stopped.”

Peace Pledge Union’s Geoff Tibbs said the British government is pushing the world one step closer to all-out nuclear war between Russia and Nato by allowing Ukraine to use British missiles inside Russia.

“Around the globe we are seeing more violence and instability than at any other time this century,” he added.

“We urgently need solutions based on peace talks, de-escalation and disarmament.”

He said Sir Keir’s ramping up of military tensions with Russia will do “nothing to shorten the war or deter Putin’s aggression,” urging ministers to listen to peace activists and the growing numbers of conscientious objectors in both Ukraine and Russia instead.

A spokeswoman for Momentum said: “The war in Ukraine has already led to hundreds of thousands of Ukrainians being killed and injured.

“Reckless military escalation by the West will only prolong the war and deepen Ukrainians’ suffering, as well as drastically increasing the danger of a nuclear confrontation.

“The government must embark on serious attempts to achieve a negotiated peace, while drawing down military spending in favour of our underfunded public services.”

The hand-in followed the US and Britain allowing Ukraine to fire long-range Army Tactical Missile Systems and Storm Shadow missiles at Russian territory.

This saw Russia lower the threshold for nuclear use and its launching of a new hypersonic ballistic missile for the first time on the battlefield.

The letter was signed by MPs Diane Abbott, Jeremy Corbyn, Ayoub Khan, Shockat Adam and Iqbal Mohamed.