Sir Keir Starmer is becoming lethal. He speaks in the puzzled tone of a reasonable man who discovers that the Government has contradicted itself.

So he wondered why until the 12th March the Government advised that it was “very unlikely that people receiving care in a care home will become infected”.

Boris Johnson was incautious enough to reply, “No, Mr Speaker, the advice didn’t say that.” Starmer was “surprised the Prime Minister queries the advice of his own Government”, and Twitter was soon alive with chapter and verse suggesting Starmer rather than Johnson was correct.

Perhaps even more damaging was Starmer’s observation that after seven weeks of publishing international comparisons at the Downing Street press conferences, the Government yesterday stopped publishing them: “Why?”

Johnson said he was “advised” that international comparisons are “premature”. But in that case, why publish them for seven weeks?

Jeremy Corbyn tried to show that the Government was immoral. Starmer makes the much more damaging charge that it is incompetent.

For Corbyn appealed to a Bennite morality which is not generally shared. Starmer, by contrast, appeals to standards which have been set by the Government itself, and shows how these have been contradicted.

Like the man on the Clapham omnibus, or in Starmer’s case the man on the Camden omnibus, he studies the official account, and points out that it does not make sense.

In April, Starmer pointed out, there were 18,000 more deaths in care homes than the average for that month for the last five years, and so far only 8,000 of those deaths have been attributed to Covid-19.

What caused the other 10,000 deaths? “The Government must have looked into that.”

Johnson agreed that “sorting the problem in care homes is going to be absolutely critical”, and ended his reply: “We must fix it and we will.”

If the problem is not fixed, we can expect to hear that assurance quoted back at the PM by Starmer.

Meanwhile, Johnson has a PMQs problem to fix.