Mr. Johnson said this week that Britain would begin testing health care workers. On Tuesday, the government said it would also provide hotel rooms to doctors and nurses who would otherwise be forced to self-isolate for 14 days because a family member at home had symptoms of the virus.

But widespread testing has not yet begun, and the health service has yet to set out the criteria or procedures.

Doctors are also suspicious of downward revisions in the level of protective gear that the government had recommended.

Health officials initially advised workers to wear a full-body suit including an airtight mask, visor and double gloves. But the service now says most health care workers handling coronavirus patients need only a standard face mask, gloves and an apron.

“They’re saying it’s evidence-based, but I think it’s also quite pragmatic,” said Dr. Gardiner of St Mary’s Hospital. “They’re running out of protective equipment.”

For now, doctors said they were largely trying to keep their fears to themselves.

“We are frightened,” said Roshana Mehdian, a trauma and orthopedic surgeon in London. “But at the same time we have to keep up a stern resolve. People are looking to the N.H.S. in hope, and we don’t want to feed into the panic.”

Tariq Panja contributed reporting.