Some experts also said the scientists suffered from a lack of independence. While Professor Vallance has begun to show some daylight with the government — he recently said SAGE would re-examine the government’s decision not to advise people to wear masks — his regular public appearances next to Mr. Johnson and other cabinet ministers have made him look too much like an agent of the government rather than an independent adviser, according to critics.

On Thursday, the government said it would consider the latest scientific advice on masks and it seemed likely to encourage their use — a decision complicated by the shortage of masks for people who work in hospitals and nursing homes.

Some of SAGE’s internal debates play out in competing research studies published by their authors. A few days after Imperial College released its dire projections about the deadliness of the virus, a team at Oxford University published a study that considered a scenario in which more than half of the population might already have been infected — a theory that, if valid, would argue for a less draconian response.

Scientists, of course, often disagree and change their minds, based on new data. To some, that is yet another argument for lifting the veil on the advisory group.

“The idea that a small group of experts can never make a mistake or miss out on any information is never right,” said Sarah Wollaston, a former chairwoman of the House of Commons Health Select Committee. “But you can’t challenge the advice if other experts can’t see what they are looking at.”

Sheri Fink contributed reporting from New York. Anna Joyce contributed research from Dublin.