Boris Johnson has insisted a Covid-19 vaccine “cannot be taken for granted”, as he ruled out smaller local lockdowns to contain the virus.
The Prime Minister told MPs there is a “good chance” of developing a vaccine before sounding a note of caution.
He also faced demands from Tory backbenchers to trust Britons to act responsibly and not leave areas in a “permanent state” with restrictions in place.
His remarks came during a lengthy Commons grilling after he announced the new three-tier approach to deal with the spread of coronavirus.
Tory former minister Steve Baker asked: “By when does (Mr Johnson) expect to have vaccinated the vulnerable population, what is his confidence in that date and why does he have that confidence?”
Mr Johnson replied: “Alas, I can’t give him a date by which I can promise confidently that we will have a vaccine.
“There are some very hopeful signs not least from the Oxford AstraZeneca trials that are being conducted.
“But, as he knows, Sars took place 18 years ago, we still don’t have a vaccine for Sars.
“I don’t wish to depress him, but we must be realistic about this.
“There is a good chance of a vaccine, but it cannot be taken for granted.”
Conservative Caroline Ansell (Eastbourne) welcomed the measures but raised concerns about the “hard hit” hospitality sector, adding: “So can I ask (Mr Johnson) what moves there might be to going forward to hyper-localised actions and what support there will be for my constituents’ jobs and businesses?”
The Prime Minister said: “It would be a wonderful thing if we could hyper localise actions in the way she suggests, alas the disease being what it is, you cannot reduce the areas in which we place restrictions too small.
“The best thing her constituents can do and the best thing the whole country can do to get through this as fast as possible is to follow the package of measures that we’ve set out.”
Sir Graham Brady (Altrincham and Sale West), the chairman of the backbench Tory 1922 Committee, added: “The Prime Minister has said there will be a four-week sunset for areas in the highest restrictions.
“What reassurance can he give to areas in Tiers 1 and 2, some of which have had additional restrictions already for two and a half months, that this isn’t going to become a permanent state?”
Mr Johnson responded: “We keep all these things under constant review and nothing could be more attractive to the Government than moving the whole country out of the present restrictions that we’re in as fast as possible.
“That requires us all to follow the guidance.”
Philip Davies, Conservative MP for Shipley, called on Mr Johnson to “once again put his trust” in Britons.
He said: “Instead of a constant blizzard of arbitrary rules which will only serve to collapse the economy and destroy businesses and jobs, will he instead remind people what’s important, social distancing, washing hands, the groups who are most at risk, the elderly, people with health conditions etc and once again put his trust in the British people to act responsibly.
“After all, believing that individuals make better decisions for themselves, their families and their communities than the state can make for them is surely at the heart of what it means to be a Conservative?”
Mr Johnson replied: “He is exactly right and the best decision that individuals can make for themselves, for their families and for communities is to follow the guidance, wash your hands, face, space, protect the NHS and save lives.”
SNP Westminster leader Ian Blackford warned against delays in Covid-19 testing and suggested a U-turn should come via an extension of the full furlough scheme to help workers.
He earlier told the Commons: “We know we’re at a tipping point, so today must be a turning point.
“A turning point where we must once again act collectively and get back to the absolute priority of suppressing the virus, protecting the NHS and saving lives.”