This was Theresa May’s best day in the Commons for a long time, and Jeremy Corbyn’s worst.

The Prime Minister expressed to perfection the anger felt on all sides of the House at Russia’s contempt for the rule of law in this country, so clearly demonstrated by the use of a Russian-made military-grade nerve agent in Salisbury.

May has long experience as Home Secretary of dealing in a sombre and deliberate manner with questions of national security which arouse the deepest feelings of indignation.

Corbyn has long experience as a backbench MP of raising unpopular points and challenging the patriotic consensus.

Any backbencher has the right to do that, and may even be admired for doing it. But for the Leader of the Opposition to do so is a grotesque dereliction of duty.

For he defied the very people he is supposed to be leading, namely his own MPs. Labour member after Labour member sided in the clearest and most trenchant terms with May rather than Corbyn.

His conduct was a betrayal of his colleagues at Westminster. Corbyn has every right to dissent from the national consensus on this question, and to side with his adviser, Seumas Milne, who continued outside the Chamber to make pro-Russian debating points.

But Corbyn does not have the right to do this while leading a parliamentary party which is embarrassed and appalled by his stance. As he does so, one can see him congratulating himself on his courage and on being the one just man at Westminster. But it would be more accurate to say that he is cut off from his own MPs by his impervious vanity, which leads him into self-indulgent blunders.

So this was May’s day. She showed judgment and grew in stature. She did nothing in hot blood. It was all very considered and proportionate, and all the more convincing for that. At last she looks like a Prime Minister who is finding her feet.