What measures could the West take if there was a nuclear strike and what would it mean for Putin?

Ian Bond, from the Centre for European Reform, says the West needs to stop being - and sounding - afraid of a nuclear attack."Nothing is as provocative to Putin as weakness, so the more the West says 'We are afraid that Russia might use nuclear weapons', the more likely that Putin is to continue making the threat of using nuclear weapons - and perhaps even use one or two to demonstrate he really means it."

Bond says the message to Russia, which could be delivered privately, should be: "Please understand that if you go nuclear, we will regard the gloves as being off."

While accepting that no one could "absolutely rule out" Russia using nuclear weapons, he added: "We should stop frightening ourselves with the Bogeyman that if the Ukrainians drive the Russians out, the Russians are going to go nuclear, I just don't buy that."