The news, delivered by chief medical officer Chris Whitty at a crunch videoconference on Saturday, was a key factor in the controversial decision to remove Spain from the list of countries exempted from 14-day self-isolation rules.
Ministers also heard that Spain’s overall infection rate per 100,000 people was running at three times the level in the UK and well above other popular holiday destinations like Greece, Italy and France.
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The renewed quarantine has disrupted millions of holidays – including transport secretary Grant Shapps’ planned break – and sparked a diplomatic row, with Spain’s prime minister Pedro Sanchez denouncing it as “unjust”.
Mr Sanchez said it was an “error” for the UK to impose blanket measures on all parts of Spain, including holiday islands hundreds of miles from the mainland, at a time when many parts of the country are experiencing lower numbers of Covid-19 cases than Britain.
A source with knowledge of the key meeting of the cabinet’s CO (coronavirus operations) committee told the Daily Telegraph that Prof Whitty said that the number of Britons testing positive within 14 days of Spanish holidays was “statistically significant enough to cause concern”, even though it only made up a small part of the total new cases, currently running at around 6-700 a day in the UK.
Ministers were also said to be concerned that nightclubs remained open in many areas of Spain, while a ban remains in place in the UK.
Around a third of 281 outbreaks identified by Spanish authorities are understood to be linked to social gatherings including nightclubs.
The source said: “Ahead of the meeting, Chris Whitty had already made it clear that he was going to say that doing nothing wasn’t an option. It wasn’t so much that the rate of transmission had increased over the previous three days, it was that there were quite a few cases of Britons coming back from Spain with the virus that was the clincher.”
However, a separate government source played down the decisive role of the 10 positive cases among returning holidaymakers, pointing instead to figures showing evidence of a second wave of Covid-19 in Spain.
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Figures released today by the European Centre for Disease Prevention and Control showed that Spain has recorded 47.2 new Covid cases per 100,000 population over the past 14 days.
This compares with 15 for the UK, 16 for France, 8.8 in Germany, 5.1 in Italy and 3.7 in Greece.
Infection rates for every 100,000 inhabitants were highest in the Aragon region, at over 120, as well as Catalonia and Navarre, where the figure was between 60 and 119.