Vladimir Putin’s forces in Ukraine are running out of weapons and ordinary Russians can now see that his invasion is badly misjudged, according to a senior British spy chief.

Sir Jeremy Fleming, head of British cyber intelligence unit GCHQ, called the decision to invade a “high-stakes strategy” where “the costs to Russia — in people and equipment — are staggering” and the “Russian population has started to understand that”.

“We know — and Russian commanders on the ground know — that their supplies and munitions are running out,” Fleming said. “Russia’s forces are exhausted. The use of prisoners to reinforce, and now the mobilization of tens of thousands of inexperienced conscripts, speaks of a desperate situation.”

The GCHQ chief added that the Russian population is “fleeing the draft, realizing they can no longer travel. They know their access to modern technologies and external influences will be drastically restricted. And they are feeling the extent of the dreadful human cost of his [Putin’s] war of choice”.

According to an independent survey by Russian polling organization the Levada Center, almost half of polled Russians are anxious about mobilisation although support for the Kremlin’s military actions remains high. The poll was published on September 1.

Fleming’s remarks come after Russia launched a series of missile attacks on Ukrainian cities which Putin said was retaliation for the explosion over the weekend that collapsed part of the Kerch bridge connecting Russia and the occupied Crimean peninsula.

“Russia, as we’ve seen in the dreadful [missile] attacks . . . still has a very capable military machine. It can launch weapons. It has deep deep stocks and expertise and yet, it is very broadly stretched in Ukraine,” Fleming told the BBC on Tuesday.

Fleming’s comments form part of a longer speech he is due to make on Tuesday to the Royal United Services Institute think-tank, in which the spy chief will also lay out the technological threat posed by China.