On Saturday, it was announced all travellers arriving in England will be required to take a Covid-19 pre-departure test from Tuesday – while Nigeria is being added to the Government’s travel red list.
Ministers said the extra test was intended to be a temporary measure following new data showing an increase in the number of cases of the new strain linked to foreign travel.
But Professor Mark Woolhouse, who is a member of the Scientific Pandemic Influenza Group on Modelling (Spi-M) which advises the Government, said the measures would not make a “material difference” as the variant is already “spreading pretty rapidly”.
He told BBC One’s Andrew Marr Show on Sunday: “I think that may be a case of shutting the stable door after the horse has bolted.
“If Omicron is here in the UK, and it certainly is, if there’s community transmission in the UK, and it certainly looks that way, then it’s that community transmission that will drive a next wave.
“The cases that are being imported are important, we want to detect those and isolate any positive cases we find, as we would for any case anywhere.
“But I think it’s too late to make a material difference to the course of the Omicron wave, if we’re going to have one.”
The UK Health Security Agency said a further 86 cases of Omicron had been confirmed in the UK on Sunday, 68 in England and 18 in Scotland, bringing the total to 246.
The travel industry reacted with fury after the latest measures were announced, despite ministers insisting they were only “temporary”.
Deputy Prime Minister Dominic Raab told Sky News’s Trevor Phillips On Sunday programme: “I know that is a burden for the travel industry but we have made huge, huge strides in this country.
“We have got to take the measures targeted forensically to stop the new variant seeding in this country to create a bigger problem.
“We have taken a balanced approach but we are always alert to extra risk that takes us back not forward.”
Prof Woolhouse said although the numbers of people with the Omicron variant are “still quite small” and likely remain in the hundreds, they are “growing quite fast”.
However, he insisted that vaccinations will still be “very, very good” at protecting against the new variant.
Statistician Professor Sir David Spiegelhalter told Sky News’s Trevor Phillips On Sunday programme: “It’s a very difficult situation because we haven’t got a lot of data yet at all, almost nothing from this country about what the risks are.
“In South Africa there’s data coming out showing pretty strong evidence that the increased risk of transmission and some evidence about people going to hospital, but it may actually be milder but we haven’t got enough data yet to be able to say.
“It doesn’t look as if it’s really severe if you get it, I think that’s about all we can say at the moment.”
Asked if measures to combat the spread of Omicron have gone far enough, Prof Sir David added: “It’s best to be precautionary, when there’s so much we don’t know… and when we don’t know it’s better to be safe than sorry.”