Seldom has a British government’s budget been rendered so out of date and so irrelevant as Rishi Sunak’s first.

One of the best indicators of this was provided in his post-budget evidence to the Treasury select committee last week by Robert Chote, the much-respected chairman of the Office for Budget Responsibility (OBR). The OBR is the independent watchdog on government spending and taxation plans – the setting-up of which was one of the few acts of Chancellor George Osborne of which I approved.

Before the budget, the OBR does its best to provide the forecasts on which the budget judgment is based. One of its obvious worries during the 2019 election campaign – goodness, was it as recent as that? – was that the two main parties were committing themselves to spending plans that implied the need for increases in taxation that they regarded as politically anathema.

Even before the escalation of fears about the coronavirus epidemic, the OBR had grave concerns about the implication of Brexit for the economy’s growth, productivity and tax revenues. But the implications of the virus for the nation’s medical and economic health have become so drastic – in such a short time – that in the light of “events” the OBR has had to change its tune dramatically.

What we are facing, indeed already experiencing, is a fall in output – gross domestic product – of anything between 10 and 20% in the next three months, according to Capital Economics, a consultancy with a well established reputation.

Why? Because the emergency declared by the government implies a collapse of demand for all but essential supplies, as the nation confronts what economists call a “supply shock” – factories closing or going on “short time” – while at the same time the level of consumer spending (ie by people like you and me) plummets as incomes collapse and so many of us are confined to our homes (in economists’ jargon, “a demand shock”).

Now, the budget was already seriously inadequate in that, despite stealing Labour’s clothes on certain public spending plans, it hardly dealt with the need to address the appalling erosion of the social services under the ill-conceived austerity strategy embarked on by Osborne in 2010.

What the OBR has recognised, in common with others, is that this is a serious emergency, which demands good judgment, not the usual obsession with deficit and debt levels in relation to GDP. The 2008 financial crisis was terrible, but it had nothing like the impact on output, incomes and employment threatened by the coronavirus pan-panic that now confronts us. As Chote said: “This is not the time to be squeamish about one-off additions to public sector debt … it’s more like a wartime situation.” He added that it was “no abdication of budget responsibility to be spending what you need to spend to deal with this”.

As it is, despite being faced with this calamitous virus – for which the austerity-struck NHS was hopelessly ill-prepared – the Brexiters who control the government seem at the time of writing hell-bent on not seeking an extension of the period for Brexit negotiations.

One suspects, however, that they will almost certainly have an extension forced upon them. Unless, of course, they crash out, which increasingly seems to be the danger.

Meanwhile, is it not wonderfully ironic that objections to freedom of movement were a vital factor in the Brexit vote, yet, while EU countries have temporarily suspended freedom of movement in response to the crisis, the British government did not clamp down and, in effect, invited more of the virus in.

Just to add to their borderline insanity, the Brexiters are also determined to leave the sensible organisations that link this country to the EU in cooperation on healthcare. When it finally became clear that we were indeed leaving the EU, one well-meaning friend suggested that I stop writing about Brexit. What? Stop opposing self-harm? Sorry. No!

And now we have coronavirus. Some believe its presence will be felt for a long time, others that its consequences will be short-lived. Who knows? But we have to conduct as good a rescue operation as possible. And it looks, with Friday’s announcement of 80% compensation for wage losses, as if the government has finally been shamed into it. Meanwhile, I am reminded of Alexander Pope’s lines: “Who shall decide when doctors disagree, And soundest casuists doubt, like you and me?”