Vladimir Putin could “risk it all” to push westwards in Ukraine with chemical weapons that would threaten his place in the Kremlin, a leading chemical weapons expert has told Express.co.uk.

Last month, Russia said it would “radically reduce military activity” around north Ukraine, including near Kyiv and the city of Chernihiv, as peace talks struggled in Istanbul. Alexander Fomin, Russia’s deputy defence minister, said the gesture was to “increase mutual trust, create the right conditions for future negotiations and reach the final aim of signing a peace deal with Ukraine”.

But this came after the Kremlin said it was moving to consolidate its hold on the eastern Donbas region, currently under pro-Moscow control.

Sergei Shoigu, Russia’s defence minister, said Russia’s “main goal” was now the “liberation” of the region.

But Moscow’s ability to creep further westward as attritional fighting continues may be in doubt without resorting to chemical weapons, the former head of the British Army’s Chemical Weapons Unit has said.

Colonel Hamish de Bretton-Gordon told Express.co.uk that the choice came down to whether Putin was willing to “risk it all” and launch unconventional assaults on Western Ukraine, or decide the Donbas “satisfies his requirements”.