One, two, three...and you’re back in the room.

Can it really be the case that after five years of factional warfare, activism rather than opposition and an embarrassingly awful leader that cost two elections and millions of votes, Labour has returned, just like that, as a credible force in UK politics? To the relief of many, the answer appears to be yes.

As we all now understand, everything can change in a flash. And the landslide election of Sir Keir Starmer as Labour leader on Saturday has already transformed a party that just four months ago experienced its biggest electoral trouncing in living memory.

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Most fundamentally, it means Labour can return to government-in-waiting rather than student politics mode, fronted at last by a leader that has the skills and potential to sell a credible manifesto to large and diverse parts of the electorate in England and Wales. Sir Keir will be far more acceptable to many – including many Scots – than either the current Prime Minister or Mr Corbyn.

A proper adult is back in charge of the Labour Party and it’s not a moment too soon.

The ousted Labour Left may never cease its messianic rantings and conspiracy theories about Mr Corbyn. Predictable mud around Sir Keir being “the new Tony Blair” (lest we forget, the last Labour leader to actually win power) is already being slung from some quarters.

But, as the Tories’ handbrake turn on the role of the state has demonstrated over the last few weeks, all ideological bets are off. Which wing of Labour Sir Keir belongs to is woefully irrelevant. Likewise, his views on a second independence referendum are now of limited immediate interest.

Response to the coronavirus and the economic aftermath are going to be the only items on the political agenda in every part of the UK in the weeks, months and years to come. And the new Labour leader is up to this Herculean challenge.

When all that really matters is keeping folk indoors, ensuring the NHS has the resources it needs and making sure the population is able to keep a roof over its head, there is a reduced appetite for party politics.

READ MORE: Labour leader Sir Keir Starmer to create ‘balanced’ shadow cabinet

Usually health funding and welfare are the ultimate party political footballs; right now, it doesn’t matter to most who is in charge, so long as they show leadership and take the right decisions.

But, as Boris Johnson and his Cabinet are discovering, such special dispensations from the electorate don’t make responding to a crisis of eye-watering proportions much easier.

Sir Keir, the 57 year-old former director of public prosecutions in England and far and away Labour’s strongest, most articulate performer during the Brexit debacle, has already set the right tone by making clear he will work with the Government during this time of national crisis while holding its increasingly worrying failings to account.

The next two to three weeks may well define Mr Johnson’s premiership; how well the NHS copes under unthinkable pressures, how many people die, the introduction of mass testing, when and how social distancing restrictions can start to be lifted, are crucially important matters to all of us. How the Prime Minister personally handles all of these issues will be intensely scrutinised. How Sir Keir responds is also key.

As we have seen during far less fraught moments than this, public confidence can turn on a sixpence. If a week used to be a long time in politics, we now know it is a potentially game-changing aeon during a global pandemic.

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And, as many have already pointed out, this is not the sort of life-or death situation jocular, shallow Mr Johnson is well-suited to. Nicola Sturgeon has shown that a sober, articulate, authoritative approach wins public trust. I expect Sir Keir, a former human rights lawyer who has also shown these qualities, will follow.

Was it a coincidence that Mr Johnson approached opposition leaders asking for co-operation on the very day Sir Keir was chosen to lead his party? The PM and his advisors will doubtless be unnerved at the thought of a capable, effective opposition demanding answers; this is not something Mr Johnson and his government have had to face so far.

The rest of us, meanwhile, should feel mightily relieved, no matter how we voted in December. This is not the moment for business-as-usual political point scoring. But there has never been a greater need for forensic scrutiny of government policy. Sir Keir is the right choice at the time.