A campaign calling for volunteers to help the NHS in the event of a major coronavirus outbreak will be launched as part of a "battle plan" against the virus led by Boris Johnson.

On Tuesday, the Prime Minister will set out the steps that could be taken if the virus continues to spread after warning on Monday that a "significant" rise in cases in Britain was "clearly on the cards".

Cancellation of mass gatherings, efforts to dissuade the public from needless travel and the use of retired medics are among emergency measures that could be brought in if the outbreak continues to worsen.

The plan will say that efforts to support the NHS could see retired doctors and nurses being called back into service, along with an expansion in the use of volunteers, enabling doctors to focus on clinical care.

The Red Cross said it had been in discussions with the Government and the NHS since the outbreak began about the help its volunteers might be able to offer.

Health officials stressed that there was no need to take such steps now but urged the public to be prepared to respond quickly if the measures become necessary.

It came as the number of cases diagnosed in the UK rose to 39, with new cases in Hertfordshire, Devon and Kent. Several schools were closed as part of attempts to stem the spread.

Ministers have warned that the crisis is set to last for "months not weeks", with officials saying widespread infection in the UK is "now highly likely".