Ministers breached their own guidance by failing to wear face masks in the House of Commons during a debate on Afghanistan on Wednesday, a Sage scientist has said.

       Prof Peter Openshaw said the Commons chamber – which on Wednesday was at its busiest since last March – “clearly” comes under government guidance that face coverings are recommended in crowded and enclosed spaces.

       Photos of the debate showed that the majority of Conservative MPs did not wear masks, with Theresa May and Jeremy Hunt among the few who opted to wear one. On the opposition benches, almost all MPs wore face coverings.

       Prof Openshaw told Times Radio: “I think what was evident is those crowded conditions in the House of Commons clearly fell into the guidance which is being given by the Government, which is that you should wear masks in crowded spaces."

       Asked whether the public was getting mixed messages, he said: "I think also the Government is getting different messages from different quarters.

       "The message that is coming through from the scientists, I hope, is one of continued caution – but of course they’re under a lot of pressure from many who represent vital businesses that, actually, we’ve got to get on and return to normal life, and I don’t envy the Government having to balance these very, very loud voices from different sides."

       Sir Lindsay Hoyle, the Commons Speaker, has encouraged MPs to wear masks in the Commons chamber but admitted he cannot force them to do so.

       The news came as Parliament’s unions wrote to Sir Lindsay asking for a clarification of the rules on masks and reported an “uptick” in Covid cases among security staff.

       The unions cited MPs who had chosen not to wear a mask on Wednesday as evidence that the rules were not clear enough.

       Security staff have been instructed to take a Covid test and wear a face covering at all times, while signs around the Palace of Westminster encourage political staff, journalists and MPs to do the same.

       A change to Parliament’s standing orders that allowed members to dial into debates remotely has now expired, making tightly-packed sessions in the Commons likely when MPs return from recess next month.

       There is no longer any legal requirement to use a face covering, but the Government has suggested that people choose to wear one when they are close to others in unventilated spaces.

       On Wednesday, a House of Commons Commission spokesman said: “Under the current public health risk assessment for Parliament, everyone should also wear a face covering when travelling around the estate, entering and leaving catering venues and in crowded spaces, unless there is an exemption.”