The final stage of the lifting of coronavirus lockdown restrictions across England could face “serious disruption” due to the India variant, the prime minister has warned, as he announced plans to accelerate the vaccine programme to curb its spread. Boris Johnson said the gap between the first and second Covid jab would be cut from 12 weeks to eight for all over-50s and the clinically vulnerable, admitting: “The race between our vaccine programme and the virus may be about to become a great deal tighter.” He announced that the army would be deployed to two variant hotspots – Bolton and Blackburn with Darwen – to help with vaccinations, and urged residents in those areas to “think twice” before taking advantages of the freedoms allowed again from Monday. Johnson said plans to ease restrictions on 17 May – allowing people to meet in groups of six indoors – would go ahead, but that the variant “could make it more difficult” for the final stage of unlocking to proceed on 21 June. He said the India variant appeared to be “more transmissible” than the dominant strain in the UK, which originated in Kent, but that it was not yet clear by how much. If it is significantly more, then, he warned, “we’re likely to face some hard choices”. “I have to level with you that this new variant could pose a serious disruption to our progress and could make it more difficult to move to step four in June,” Johnson said. Asked whether the lockdown easing would have to be paused during a press conference, he added: “The truth is, we cannot say for certain … The situation is very different from last year, we are in the throes of an incredible vaccine rollout … We just have to wait and see … We rule nothing out.” The PM’s words came as new documents released by the Scientific Advisory Group for Emergencies (Sage) revealed just how worried scientists are about the variant. Modelling by Sage suggested it was “a realistic possibility” that it could be up to 50% more transmissible than the Kent variant. If that was the case, they said, progressing to stage 3 of the road map – due on Monday – would “lead to a substantial resurgence of hospitalisations (similar to, or larger than, previous peaks)”. The variant’s spread will raise questions about perceived government delays in adding India to the “red list” of countries from which arrivals have to quarantine in hotels. Johnson’s announcement came following calls from councils in Lancashire and Greater Manchester to let them roll out vaccines to all over-18s in some variant hotspots, including Bolton and Blackburn with Darwen. Prof Chris Whitty, England’s chief medical officer, said said the “majority view” of the Joint Committee on Vaccination and Immunisation (JCVI) was that this approach would be a “net disadvantage”. However, councillor Andy Morgan, Bolton council’s cabinet member for adult social services, insisted the council had been given some “flexibility” to vaccinate younger people, and would be offering vaccines to all over-18s in the three worst-affected wards from Saturday. “Our interpretation of the guidance is that we can start to vaccinate 18s and over in BL3 [the affected postcode] tomorrow, subject to vaccination supply,” he said. “We’ve got some flexibility locally to surge-vaccinate, but the biggest thing for Bolton is not being locked down, which would have been devastating for the town. David Greenhalgh [Bolton’s council leader] has been lobbying every man and a dog all day on that, so we are relieved,” said Morgan. Despite the councillor’s confidence, local politicians have no jurisdiction over vaccination centres. Bolton’s clinical commissioning group runs the district’s eight sites and it is not clear which guidance they will follow. A spokeswoman for Bolton clinical commissioning group suggested there would be no immediate offer of vaccinations to over-18s. “We continue to follow the JCVI guidelines,” she said. Dominic Harrison, the director of public health for Blackburn with Darwen council, said he was extremely disappointed that the government had not given the go-ahead to vaccinating all over-16s in the worst-hit neighbourhoods. He told the Guardian: “It just seems that failing to do all we can in the areas that have the highest rates now is a lost opportunity and we will be saying that to ministers on Monday. What we still haven’t got is a clear national strategy for managing importations and outbreaks of new variants at a local level. There just is no strategy. “It feels like we are making it up on the hoof and you’ve now got Scotland and England giving two different plans of action on the basis of very similar data.” Responding to the spread of the India variant in Scotland, the first minister, Nicola Sturgeon, announced that infection rates in Glasgow and Moray meant the areas would remain on level 3 restrictions while the rest of the mainland dropped to level 2 on Monday, which means hugging loved ones and meeting indoors is allowed. She said she was “pretty sure” that the vaccination programme in Scotland would be accelerated, but that she was waiting for advice from the JCVI. The Welsh first minister, Mark Drakeford, also said he had decided against liberalising rules that would have let more people mix and some small public events go ahead. The chief executive of the NHS Confederation, Danny Mortimer, on Friday called for the government to “look at measures around lifting lockdown”. He said ministers should consider whether allowing international travel from 17 May should be “rethought” and giving greater financial support to those who test positive to encourage them to self-isolate. New figures from the Office for National Statistics on Friday showed the number of infected people across the UK continued to fall, but the R number – the average number of people someone with Covid is estimated to pass it on to – rose slightly in England to 0.8-1.1. A Guardian analysis of Public Health England data shows overall Covid cases have risen in four out of 10 UK local authorities in the week to 8 May, with some areas seeing steep rises. The analysis found 151 of 382 local authorities had higher weekly case rates per 100,000 residents compared with the previous seven days, accounting for 39.5% of all areas. Of these, 97 councils had seen cases rise for two consecutive weeks.