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