The Chief of the Defence Staff has told the armed forces to plan for a six-month Coronavirus operation and warned of threats from “those who wish to undermine our way of life”.

In a letter issued to senior officers, General Sir Nick Carter has said the armed forces should treat the military response to the Coronavirus as a six-month operational tour.

He also warned against complacency, saying the focus on the military aid to civil authorities should not detract from the threat posed to the country from hostile states and terrorist groups.

General Carter said in the note: “the indications are that this disease will spike around late May and early June.

“We are to be prepared for our collective posture to be on an operational footing by mid-April, recognising that this could endure for six months or so.”

The Service chiefs and the head of Strategic Command are expected to respond early next week detailing what each can provide for Operation Rescript, the codename for the military response to Covid-19. A leave ban for some personnel is expected.

The operation, comprising up to 20,000 military personnel, will be run from the Standing Joint Command based in Aldershot, the Headquarters responsible for UK resilience operations in support of government departments other than the MoD.

In his note, seen by the BBC, the head of the armed forces says: “we must also assure our ability to protect ourselves, recognising that times of national emergency are also opportunities for those who wish to undermine our way of life”.

He acknowledged the unprecedented situation was “unsettling for individuals and families”.

“This is a time for leaders to step up and deliver,” he said. “As I have often said in the past - we need to be prepared to fight the war we may have to fight and it is now clear that moment has arrived.”

Tobias Ellwood, chairman of the defence select committee, said it was crucial sea deterrence and Nato commitments were maintained whilst the UK worked to contain the coronavirus pandemic, as such a situation presented a prime opportunity for attacks to be carried out.

“We must acknowledge we are going through a chaotic period and that is when we are most vulnerable,” he said.

“There will be non-state actors who will continue to wish us harm and it is when the international community is focused elsewhere that terrorist incidents occur.”

He added that it was imperative the safety of Britain was not sacrificed as the Government looked to protect the UK against coronavirus.

Meanwhile Bob Seely, a member of the Foreign Affairs Committee, said it was "very reasonable" that efforts were being stepped up to challenge outside threats whilst the main focus is on tackling the pandemic.

"It's contingency planning,” he said. “The military will be getting training in place now. They have got to be prepared and plan to keep people safe to make sure things run smoothly.

“It's about planning for problems so then you are ready for any eventuality. The army will be ready to deal with whatever they have to do and they will do it well."