At any rate, Nukes are regarded as cheaper than conventional forces. Our current army is puny compared to the Cold War era, when their population was ~260m (in 1979), down to 143m, post breakup, compared to our 60-70m. We lack the numbers to bring the conflict to a ceasefire but nukes make up for that weakness.
In reality, of course, other nations should (*should* but no actual compulsion, viz Ukraine) come to our side. But that's when war gets really ugly, when neither side is strong enough to win but the frontline continues with its meat-grinder routine, as with World War I.
If Corbyn had prefixed his nuke stance with "I can not conceive of conventional war breaking out in Europe ever again", then what he went on to say would have made sense (to me, at least) but he did not. Instead, he practically said "please invade us, I will not stop you, I've always wanted to be a forelock-tugging Russian serf."