Michelle O'Neill and John O'Dowd have just made greater cross-border co-operation on coronavirus more, not less, difficult to achieve

It was an important moment. It was known that, on other issues, there were tensions and divisions between the parties, so seeing them together and committing to a joint response was of huge significance.

A sign, perhaps, that when it came to an extraordinary moment and an extraordinary crisis, political parties could shift from the usual 'dreary steeples' domain and work together for the common good.

Yet less than 24 hours later Michelle O'Neill called her own press conference in the Great Hall at Stormont to backtrack on a stance she had supported the previous day: "Now is the time to take action and ensure the schools, universities and colleges are closed and that needs to happen immediately. People are fearful. On the back of the angst that there is amongst the wider public, now is the time to take action. People are rightly concerned about the impacts on their families and their children and, as a parent, I share those concerns and I have been contacted by many parents who did not send their children to school this morning."

The contents of her statement don't seem to have been discussed with any other party in the Executive, let alone Health Minister Robin Swann. Indeed, they don't even seem to have been discussed with her colleague Deirdre Hargey, the Communities Minister, who had appeared on a BBC Radio Ulster interview about two hours earlier and supported what had been agreed the day before.

It's not entirely clear why O'Neill changed her position so rapidly. A number of sources suggest that Sinn Fein came under "enormous pressure" at constituency and grassroots level after Boris Johnson's press conference - on the same day as the Executive's conference - which was interpreted by some as the UK taking its own standalone 'herd' response to Covid-19, rather than sharing the advice and strategy in other affected countries.

Whatever the specific reasons, it would surely have made sense to discuss it with the Executive first, if only to gauge whether the "rapidly changing daily circumstances" relating to tackling the virus justified a recalibration of Executive policy?

It was also interesting that O'Neill chose to make her statement - effectively distancing Sinn Fein from Executive policy - the day before she and Arlene Foster were due to take part in a North-South Ministerial Council (NSMC), at which tackling the crisis was topping the agenda.

Again, why couldn't she have waited an extra day and gauged the mood at the NSMC? Why not have that particular conversation behind closed doors - at which the Irish Government side could update the Northern Ireland government about their own progress - and see if it was possible to dovetail certain aspects of their approaches?

Perhaps most important of all, why did she do something which she knew was certain to provoke a huge storm and undermine the united approach which had earned plaudits on Thursday afternoon?

If things were bad before the NSMC, they rose to toxic level late afternoon on Saturday with this tweeted intervention from Sinn Fein MLA (and former Health Minister) John O'Dowd: "Let's be clear, this shire (sic) of b******s are using everyone of us in some form of twisted medical experiment. Do you honestly believe the rest of Europe is wrong and this balloon and his ilk are right? If you are not angry, it's time to get angry, we are on the brink of disaster." That tweet, intemperate and unnecessary though it was, actually shores up the argument that it was Johnson's comments and response on Thursday that persuaded (although others would say that her hand was forced by an on-the-ground rebellion) O'Neill to backtrack from Sinn Fein's pro-Executive unity.

But why not talk to Foster and Swann and ask them if they were prepared to distance themselves from Johnson's position? Indeed, during ministerial question time yesterday Swann said: "Herd immunity is not a tool I will be utilising as a way to combat this virus."

Had O'Neill asked him about it on Friday morning she might have discovered that he would have been happy with a joint Executive statement saying then what he said 72 hours later. So, why didn't she ask him? Why didn't she speak to Education Minister Peter Weir?

She must have known, as must her advisers, that her statement on Friday was very unhelpful. But she went ahead.

She must have known that O'Dowd's tweet would offend many people, including some who agreed with his broader point, but she didn't distance herself from it, and nor does she seem to have asked him to remove the tweet.

Yesterday morning Naomi Long tweeted: "I think the politicisation of this crisis by SF is wrong. We now need to get round the table at the Executive and get back on the same page, giving consistent, clear and scientifically sound advice to those we represent to keep them as safe and as healthy as possible."

Replying to her, Sinn Fein senator (and former Lord Mayor of Belfast) Niall O Donnghaile, said: "But people dying is 'political'. Putting a political union with Britain ahead of the scientific realities of living on a separate landmass is 'political'. I don't want us all to simply be on the same page if you're on the wrong page tbh."

Sinn Fein is at the heart of government in Northern Ireland. It agreed a joint Executive strategy on Thursday and that agreement provided a rare moment of hope that something as enormous as Covid-19 could be tackled collectively. Since then the party has fallen in behind O'Neill in the ending of that collective approach.

So, does Michelle O'Neill support Robin Swann? Is Sinn Fein standing behind the efforts of the Health Department's efforts to contain and control Covid-19? And, if not, then what precisely is Sinn Fein's position at the moment?

Whether the party likes it or not, the fact remains that Northern Ireland is part of another jurisdiction and each jurisdiction has the right to decide how best to deal with this crisis. As it happens I do believe in the need to co-operate at a time like this, having noted elsewhere that the virus is no respecter of borders or national identities.

My fear is that Sinn Fein's actions since Friday morning have made north-south co-operation on this crisis much more difficult to achieve.

The Executive table is the best place to agree joint strategy - not solo-run press conferences and intemperate tweets.