Consider the timing involved, with 31st January the cutoff date.
It would've been possible for an infected European to get to our shores in the final days before 31st January, incubate the virus without symptoms appearing before mid-February, spreading it around during that time ... and, symptoms among our own people would only be appearing, NOW.
As of yet, we've had two cases out of the known 35 where our people must've contracted the virus within the UK. They've only just appeared AS cases to consider. [Which fits the pattern, I'd say ....]
The others are all our own people, UK citizens, returning to the UK from virus hotspots such as Italy, Iran, Singapore, some from China. Our biggest problem to date has been whether our own citizens are returning here, infected.
BUT ... as for what we can now do with our borders, well, we're going through a transition period between Brexit Day and working out what our precise form of relationship with Europe, in future, will be. So this isn't quite as cut-and-dried an issue as you'd think it would be !!
See this ...
https://www.gov.uk/guidance/visiting...k-after-brexit
In any case, the 'free movement of people across the EU' basically refers to the right any EU citizen had to go to work in another EU country, or to go and live in another EU country. Citizens of EU member countries can treat other EU Member State countries as though they were their own. People can still travel here as easily as before,
as tourists (except for showing a passport; necessary now, not necessary before Brexit).
The real issue is whether our people are willing to close our borders to EU people. So far, our Government has shown no willingness to do that ... all they do is issue warnings about the countries WE are advised not to visit.