Theresa May yesterday addressed the Commons on the “reckless and despicable act” committed in Salisbury. With calm deliberation she set out the damning case against the Russian state:

“Based on the positive identification of this chemical agent by world-leading experts at the Defence Science and Technology Laboratory at Porton Down, our knowledge that Russia has previously produced this agent and would still be capable of doing so, Russia’s record of conducting state-sponsored assassinations and our assessment that Russia views some defectors as legitimate targets for assassinations, the Government have concluded that it is highly likely that Russia was responsible for the act against Sergei and Yulia Skripal. There are, therefore, only two plausible explanations for what happened in Salisbury on 4 March: either this was a direct act by the Russian state against our country; or the Russian Government lost control of their potentially catastrophically damaging nerve agent and allowed it to get into the hands of others.”

Jeremy Corbyn should have agreed with her that such conduct is intolerable, and declared that the Labour Party expects the firmest action to show that Britain will not tolerate such outrages. He might, if he wished, have added that our quarrel is with the Russian state, not with the Russian people, who suffer greatly from their rulers’ lack of scruple.

But Corbyn and his advisers have a soft spot for those rulers, so he instead implied that despite this outrageous use of force on British soil, relations with Moscow should continue much as they are now. He tried to divert attention from this supine and indulgent policy by launching a diversionary attack on party funding.

Some of Corbyn’s own MPs were plainly disgusted by the way he had fallen below the level of events. Instead of speaking for the British nation, the Leader of the Opposition had indicated that Britain’s enemies would have nothing to fear from him.

The Prime Minister said that if “no credible response” is received from Moscow, she will return to the Commons to set out the full range of measures which Britain will take in response.

The likelihood of a credible response from Vladimir Putin is minimal. On Sunday, he wishes to be re-elected, which is presumably one of the reasons why this reckless and unscrupulous stunt has been committed. He has garnered a lot of publicity for a minimal outlay.

But we are not prepared to allow Salisbury, or any other part of the United Kingdom, to be used for such despicable acts. And what we do next must demonstrate the strength of our resolve.

In 1971, a Conservative government expelled 105 KGB agents from London, after Andrei Gromyko, the long-serving Soviet Foreign Minister, had repeatedly failed to respond to warnings from Sir Alec Douglas-Home, the British Foreign Secretary, about the extent of Soviet espionage activities, which had got out of hand under the previous Labour government.

Moscow was taken aback by this firm action, and protested in angry terms, but refrained from significant retaliation, for it knew Douglas-Home, who had a long record as a steely Cold War warrior, possessed a second, even longer list of Russians who would be thrown out of London if such retaliation were to occur.

The net effect of this step was to make Britain more rather than less respected by the Soviet Union, and by the wider world. The United Kingdom was not a place where Russian agents were going to be allowed to act with impunity. Just over two years later, Douglas-Home paid a visit to Moscow, and was repeatedly toasted by Gromyko.

Similar firmness of purpose must be shown on this occasion. Russian agents cannot act with impunity here. That simple message must if necessary be backed up by expulsions.