A source said: "Employers can nominate frontline staff and councils will include waste collectors, environment health officers and crematorium workers." Leeds, Rochdale and Bristol residents have had disrupted rubbish collections as council staff isolated.

       So far, supermarket depot staff have been given access to 500 sites in response to fears of food shortages, with the critical worker list expanding on Friday to include train and lorry drivers, police officers and border officials.

       A more limited relaxation of isolation rules has been announced for 16 other sectors of the economy, including transport, emergency services, the waste and water industry.

       There are believed to be between 700-900 testing sites now coming online.

       Staff in these sectors can now stay at work if they are identified as a contact of someone who has Covid-19, providing they continue to produce negative lateral flow tests.

       It is understood that Boris Johnson is pushing to more than double the number of sites in operation across the country to 2,000, meaning that more sectors can be added in the coming weeks.

       The Covid operations Cabinet subcommittee meeting will allot the remaining sites across Whitehall departments and sectors they represent.

       Policing minister Kit Malthouse suggested airline staff could also receive isolation exemptions to relieve the "pingdemic".