A coronavirus variant carrying some of the same mutations as the highly contagious British variant may have been in the US since October and already be widespread, a re-analysis of more than 2m tests suggests.

Genome sequencing to confirm whether the variant observed in Americans is the same as the so-called B117 variant currently circulating in the UK is under way.

Results are expected within days but the revelations have prompted fresh questions about where the altered virus originated, including a small possibility that it began in the US, not the UK, or elsewhere altogether. The variant has also been found in at least 17 countries, including South Korea, Spain, Australia and Canada.