The deputy chief medical officer for England has sought to explain why the UK has not implemented a screening procedure for new arrivals from abroad.
Jonathan Van-Tam, who also sits on the Scientific Advisory Group for Emergencies (SAGE), argued that a screening programme would let too many people through to be effective.
At a Number 10 press briefing, Mr Van-Tam was asked about checks at airports, however, he seemed to only address the idea of a screening programme rather than a specific testing programme.
He also argued only a small proportion of cases would come in from abroad right now compared to the wider rate on infection already in the country.
He said: 'With port of entry screening there is a basic problem that the length of a flight from a far-flung place to the UK is no more than 12 hours.
The problem is that people can be infected before they get on the flight and the incubation period for this virus is up to 14 days, and it's typically five days.
'So I can fly back on a long flight, and I can become infected in that country before I get back on the aircraft and I can sail through Heathrow with absolutely no symptoms at all. I would have nothing to declare and won't have a fever. I won't be picked out. But when I get back to my home in the north of England at that point a few days later, I might develop symptoms, so the port of entry screening has not worked.
'That's the basic mathematical problem. Right now we are in a situation where there is widespread transmission in the UK we are turning that down, but it is still there, and it has not gone away.
'So the proportion of new cases coming in form abroad even if flights were operating would be minuscule compared to the amount of force of infection moving around in our societies in the UK.
'We do at some point hope that we will turn this curve down and then we can start to think about how and when, and how carefully, we start to ease the restrictions we are under without letting the virus chase off again and all things - all scientific options - will be under consideration I am sure about that.'
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