As the massive contingency plan was pulled together to enable forces and the public to cope, the Metropolitan Police Commissioner said former officers could be brought back to boost the ranks.

Dame Cressida Dick said she had not ruled out any option as part of contingency plans including the use of volunteers.

It came as the National Police Chiefs’ Council revealed its scenario planning included up to a fifth of officers having to go off sick. Cancelling rest days and leave is the first option – but it comes at a time when officers have already had to do this due to cuts to officer numbers.

Dame Cressida said: "We need to be flexible, we are a people organisation and of course it's likely as other people are coming into contact with the virus some of my people will as well. We have had plans in place for a long time to be able to move people around, to change people from one role to another, to make sure we protect the really mission-critical services.

"We have not ruled out any option in terms of boosting our numbers. We have lots of people who volunteer with the Met, we can bring them in more, and indeed there may be some areas where it would make sense to bring in some retired officers to help us out."

Some retired officers questioned where the money would come to pay for it and whether those who had left the force because of the way they had been treated would be eager to respond.

But others were in favour as a way of quickly finding people to deal with issues such as being on hand at supermarkets.

Retired former Detective Chief Superintendent Ellie O’Connor said: “There’s a large marching army that could potentially be brought back in. There’s years and years of experience to call on. We’ve been through the riots, we’ve been through the Olympics, we’re not daft.”

"It’s got to be considered. There are many retired officers and staff that still have all their skills that could be brought back into use. They don’t have to have uniform. You could give them crimes to review or triage people at the front desks. They could be make us part of the Special Constabulary and contact us through the pension scheme. It could be done quickly and easily.”

The National Police Chiefs' Council revealed its planning included 20% of officers being ill. First steps would be mutual aid before other options were considered.

A spokesman said: "When policing is under severe strain, from either demand or capacity issues, some services will have to be reduced - that could mean historic investigations that have a low risk attached to them.

"We will always focus on core policing and serious crime and the public should expect continuity of these services."