The number of coronavirus cases in the UK has risen by 34 in a day, to a total of 85.
Twenty-nine had recently travelled to affected countries or picked it up from people known to have travelled from abroad.
But three more contracted the virus in the UK and no one knows where they got it from.
The UK’s chief medical adviser said investigations and contact tracing had begun.
Earlier, Prof Chris Whitty said onward transmission and an epidemic in the UK was “likely”.
The total number of confirmed cases in England is now 80, with three in Scotland and one in Wales and Northern Ireland.
What do I need to know about the coronavirus?
- HOW IS THE UK PLANNING FOR AN OUTBREAK: How prepared are we?
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- A VISUAL GUIDE TO THE OUTBREAK: Virus maps and charts
Boris Johnson has said that workers will get statutory sick pay from the first day they are off work to help contain the virus.
In the Commons earlier. he said people who self-isolate should not be “penalised for doing the right thing”.
That means those receiving statutory sick pay would get an extra £40.
Officials believe up to a fifth of the workforce may be off sick during the peak of an epidemic in the UK.