A further 13 patients in England have tested positive for coronavirus, bringing the total in the UK to 36.
Three of the new cases were “close contacts” of the man from Surrey who became the first to be infected within the UK rather than abroad.
Another from Essex had not travelled to any of the known hotspots and officials are investigating how they contracted the coronavirus.
Six patients had recently travelled from Italy and two had returned from Iran, according to chief medical officer Chris Whitty.
These cases are from London, West Yorkshire, Greater Manchester, Hertfordshire and Gloucestershire.
The thirteenth case is in Scotland, in a person who recently travelled from Italy.
“All are being investigated and contact tracing has begun,” Mr Whitty added.
The 50 per cent increase in cases came as health secretary Matt Hancock refused to rule out quarantining whole cities to combat the outbreak.
“There’s clearly a huge economic and social downside to that but we don’t take anything off the table at this stage because you’ve got to make sure that you have all of the tools available if that is what’s necessary,” he said.
Mr Hancock also confirmed the government were considering shutting schools or banning large gatherings such as football matches.
Willow Bank Infant School in Reading, Berkshire, announced it was closing for “some days” after a staff member tested positive for coronavirus.
In an email, headteacher Michelle Masters urged parents to “remain calm and follow the recommended hygiene procedures”.
Another Reading school, Aldryngton Primary, will close on Monday for a “deep clean” after it hosted a training event attended by a patient.
Several other European countries have also recorded sharp rises in recent days, with 117 in Germany and more than 1,000 in Italy, where 29 people have died.
France has banned indoor public gatherings of more than 5,000 people and shut down the Louvre museum.
