Ministers are coming under growing scientific and political pressure – including from the Tory benches – to prevent a “surge” in coronavirus cases connected to Christmas, as Downing Street rejected calls for any measures to mitigate the impact. Conservative MPs, scientists and doctors called for a rethink of the policy allowing three households to mix indoors over Christmas, or for schools to take longer breaks over the festive period to curb the spread of Covid, but No 10 said there were no plans for either. But with cases in London rising sharply and infection rates high in many other places, Venki Ramakrishnan, the Nobel prize-winning biologist and recently departed head of the Royal Society scientific body, warned of the expected consequences. “I understand the emotional need families have, but from a public health point of view the relaxation of rules for Christmas are simply a recipe for another surge of the virus,” he told the Guardian. “At a time when vaccines look very promising, I think that it is not too much to ask people to exercise restraint this Christmas. I myself have not seen my children or grandchildren for over a year because they live in the US, and do not expect to until we are vaccinated or infection rates are very low.” Ramakrishnan stressed he did not seek “to be prescriptive about it myself” over the rules, adding: “That is for the government. I think if restrictions are relaxed as planned, and people take advantage of relaxed rules, it will lead to another surge at a particularly bad time.” While household mixing plans for up to five days over Christmas are UK-wide (or seven days for Northern Ireland), the Welsh health minister, Vaughan Gething, said this could change in Wales. Asked at a Monday press conference if Wales could reconsider the four-nations approach to Christmas, Gething said: “You can never say never … Nothing is off the table. It depends on the choices each of us is prepared to make.” Downing Street said there were no plans to review the Christmas guidance or keep schools closed for longer. Boris Johnson faced dissent from his own backbenches on Monday. The Tory former defence minister Tobias Ellwood asked the health secretary, Matt Hancock, to review the Christmas plan “so we don’t begin the new year with a third wave”. Ellwood said in the Commons: “2020 has been the most testing of years, 2021 should be different because of that vaccine. My concern is letting down our guard for five days during Christmas could be very dangerous indeed.” Stephen Hammond, the Tory MP for Wimbledon in south-west London, called for urgent action on transmission in schools but did not argue for a change to the Christmas rules, saying this should be “a personal decision”. He said: “I think a lot of people will probably now decide that, actually, they don’t want to take that risk. So I think a lot of people will take that decision for themselves, and I think that’s probably the right way.” Labour called on Monday for the government to set out how it planned to avoid the NHS coming under intense pressure in January. “Overall increasing areas are rising faster than decreasing areas are falling,” Jonathan Ashworth, the shadow health secretary, told Hancock in Commons exchanges about the decision to move London and some neighbouring areas into the top level of coronavirus restrictions. “As things stand we are heading into the Christmas easing with diminishing headroom. The buffer zone these tiers was supposed to provide is getting much thinner.”