UK prime minister Boris Johnson on Thursday said health officials are “anxious” about the Covid-19 variant first identified in India and refused to rule out the possibility of localised lockdowns to stem its spread.

“We want to make sure we take all the prudential, cautious steps now that we could take,” Johnson said, speaking at a primary school in Ferryhill, County Durham.

“There are a range of things we could do, we’re ruling nothing out,” he said, adding that he has not seen any evidence to delay the staged lifting of England’s lockdown.

But he added: “There may be things that we have to do locally and we will not hesitate to do them if that is the advice we get.”

Scientists in the UK are desperately trying to parse limited data on the B.1.617 family of variants from India, which experts say are at least as transmissible as the UK’s homegrown “Kent” variant — B.1.1.7 — blamed for the devastating second wave of the virus that hit the UK in the winter.

There have been 1,768 sequenced cases of the most concerning strain from India, known as B.1.617.2, according to the latest data from the Covid-19 Genomics UK Consortium. It is now the second most common variant in the UK, accounting for roughly 15 per cent of virus samples sequenced over the past two weeks, up from 7 per cent one week earlier.

Chart showing that there are early signs that B.1.617.2 may be pushing the national trend in cases back upwards

According to the latest scientific modelling by government advisers, a variant that is as transmissible as the Kent variant, and which has some vaccine resistance, “could easily lead to another peak of double or treble the size of that seen in January 2021 if no interventions were taken”.

The warning contained in a paper released by the UK’s Scientific Pandemic Influenza Group on Modelling (Spi-M) on Monday concluded that “variants remain a major risk to the road map” out of lockdown.

The government’s Scientific Advisory Group on Emergencies (Sage) was due to meet on Thursday to discuss the emerging evidence on both the transmissibility and vaccine resistance of the B.1.617 variant.

One Whitehall official described the Indian variant as “the most concerning we’ve seen so far” but cautioned that “there is no panic yet”. The individual added it would not change the government’s plans to proceed with the next step of lockdown next Monday.

But some officials believe it could have an impact on the next stage on June 21. “The next week is going to be crucial. We’ll have more data and testing and that should be able to give us a sense on whether it will impact on the plans for later this summer.”

Andy Burnham, mayor of Greater Manchester, wrote to the Joint Committee on Vaccination and Immunisation (JCVI) this week to request that everyone in the region over the age of 16 be offered a vaccine to reduce transmission of the variant.

In Bolton, cases are rising fastest among young, mostly unvaccinated groups, with rates relatively flat among older and vaccinated populations.

Chart showing that cases are rising again in north-west England where B.1.617.2 is circulating, but that rise is concentrated among younger, less vaccinated age-groups

On Thursday, local public health officials in Blackburn decided to make vaccinations available to anyone over the age of 18 in three wards where the variant had spread.

The JCVI has been debating the proposal of increasing vaccine provisions to regions of the country with outbreaks of variants first identified in India, though officials said the committee’s main priority remains vaccinating the eligible groups already set out in their age-based vaccine plan and ensuring the speed of the programme is not impaired.

While some are concerned there are signs it is more transmissible than the Kent variant, others have cautioned against the overinterpretation of small pockets of data.

“We are talking about a small number of (quite large) transmission clusters contributing a disproportionate amount to these numbers so it is really noisy,” said Andrew Rambaut, professor of molecular evolution at the University of Edinburgh, on Twitter.