There is a risk that the variant first identified in India could be transmitted by people travelling out of the UK, Sir Jeremy Farrar said.
The director of the Wellcome Trust told BBC Radio 4’s Today programme: “Britain is a very connected, and very small country and the chance of local cases becoming regional and then regional becoming national is very clear.
“And it is also connected internationally and I think that’s also a concern not only for importation of new variants coming into the country, but also people travelling out of the country – there is a risk that this variant B.617 could be transmitted from the UK now.
“I think travel should still be very cautious and only when absolutely essential.
“But the only way to stop these variants occurring is to drive down transmission.”
He added: “The biggest risk to countries like the UK – who have done very well with vaccine rollout – is variants arising from anywhere in the world and then spreading around the world when they have a biological advantage.
“So driving down transmission in this country is essential, but so is it in the rest of the world, and that means driving down transmission and making vaccines available globally.”