Lord Sumption:

I cannot speak for any country other than the United Kingdom. In the United Kingdom the measures were taken under the Public Health Act, which contains - in addition to the general powers to take steps to control the spread of disease - specific provisions about restrictions on entering at ports, airports and so on. There was a clear legal basis for them. Unlike the points I made earlier about the lockdown, it seems to me that the restrictions on travel being imposed by law in the United Kingdom are within the powers of the Public Health Act. Whether they are effective or proportionate is another question altogether. It depends, at least in part, upon how effective they are in restricting the spread of the disease, a subject on which there is very little research currently available.