One of the running stories in the last week’s press has been an apparent stand-off between Priti Patel and Dominic Raab over the question of whether or not to ‘close the borders’ – i.e. restrict non-essential travel and stopping flights from countries badly afflicted by Covid-19.

It’s an issue which apparently divides the Cabinet, with the Daily Telegraph reporting that Patel was backed by Matt Hancock, the Health Secretary, and Raab by Rishi Sunak, the Chancellor, and Grant Shapps, the Transport Secretary.

For the moment, the Prime Minister appears to have come down firmly on the side of the Foreign Secretary. Is this a case of Boris Johnson’s liberal instincts triumphing over the needs of the moment, as has been alleged about his early response to the pandemic?

In truth, on this question – as on others – the Government is walking a tightrope between competing evidence and legitimate concerns. On the scientific evidence, for example, its own medical experts currently say there is no case for a travel ban.

Yet other scientists, such as the authors of this article in Science which has been highlighted by Migration Watch, suggest that travel restrictions imposed on Wuhan by the Chinese authorities did slow the spread of the disease: “We find a 77 per cent reduction in cases imported from Mainland China to other countries as a result of the Wuhan travel ban in early February.”

Likewise, fears from the Home Office and Department of Health that ongoing (even if much reduced) travel will lead to a greater number of domestic cases must be balanced against the Foreign Office’s clear concern – which will be based on feedback from diplomatic staff on the ground – that new restrictions could prompt retaliatory measures from some of the countries affected and hinder their efforts to rescue British citizens stranded overseas.

One theoretical alternative to banning flights would be on-arrival screening at airports, but there could be serious practical barriers to implementing this – not least of which is that it might increase the exposure of Border Force agents to infection at a time when the Government is already struggling to adequately supply front-line NHS staff with protective equipment.

Furthermore, staff might lack the experience to implement a rigorous and comprehensive on-entry testing system. Such a policy has apparently not been the UK’s historical response to incoming travel from areas afflicted by previous outbreaks. Without that experience of more targeted screening, instituting universal screening (albeit of a much reduced volume of incoming travellers) could pose a formidable challenge.

Ministers may also be wary about heaping even more pressure on airlines at a time when many are already clamouring for Government support, as well as putting more stress on the FCO’s special arrangements by closing commercial avenues home for Britons abroad.

There is clearly no easy answer. Yet whilst the leaking of Home Secretary’s position to the press might have angered Number Ten, what is shows us is the Cabinet system working as it should. Both Patel and Raab, speaking as they do for powerful departments with different institutional priorities, ought to be arguing hard for their preferred approaches. It is ultimately for the Prime Minister to choose which set of considerations weighs the heavier – and for the moment, the planes will fly.