Japan, Spain and France have found small numbers of infections involving a new, potentially more transmissible variant of the coronavirus, most linked to travel from the UK, where it was first detected.

The rapid spread of the variant led to the lockdown of London and southern England this week, prompted a temporary French blockade of the English Channel. Because few countries have the level of genomic surveillance that Britain does, there is concern that the variant may have been travelling across the world undetected for weeks.

So far, the British variant has been diagnosed in seven people in Japan. All had either recently travelled to the UK or been in contact with someone who had.

In Spain, the variant was found in the capital region, local authorities said. Antonio Zapatero, a regional health official, said that four cases had been confirmed in Madrid.