The government risks a rebellion from younger people hit by the coronavirus crisis if the lockdown is in place for too long, a former Bank of England governor has warned.

Mervyn King, who oversaw the bank during the 2008 financial crisis, said ministers must have an exit strategy on how to wind down the severe restrictions on daily life in order to salvage the economy when the pandemic ends.

Lord King said younger people would question why their futures were "being put at stake in order to help prolong the life expectancy of older people".

Strict measures announced last week to keep people at home are "making a difference" to the spread of the outbreak, the government's chief scientific adviser Sir Patrick Vallance has said.

But ministers are worried about ending the lockdown too early. At the weekend, Dr Jenny Harries, the deputy chief medical officer, said "all of our efforts will be wasted" if social distancing measures are relaxed too soon and warned that the UK may not fully return to normal life for up to six months.

Speaking at a Policy Exchange seminar on the coronavirus crisis, Lord King said: "The idea that we can simply maintain this lockdown for months and months on end according to the development of the virus is unrealistic.

"I think that the government needs to find an exit strategy which is going to be gradual and it may need to examine methods by which those people who have had the virus are able to go back, travel and go to work.

"I also fear that if we maintain the lockdown for too long, there will be a rebellion against it because an awful lot of younger people will say, 'Well the younger generations have suffered in the last 20 years. Why on earth is our future being put at stake in order to help prolong life expectancy of older people, whose life expectancy will not be very high in any event?'"

Lord King also urged the government to learn lessons from this crisis by ensuring there is "greater spare capacity" in the British economy to cope with other pandemics.

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Nick Macpherson, a former Treasury permanent secretary, said the government must have a credible plan for the future, including how the UK will pay for the crisis.

Lord Macpherson said: "You cannot continue in lockdown indefinitely. I would also like to think that just as during the war – and I am cautious about wartime metaphors – Beveridge was writing his report on the future of the welfare state. I hope government is actively considering how we pay for this crisis, how we come through stronger.

"The critical thing there is getting the balance between taxation, borrowing and printing money right. Needless to say, I am quite cautious about printing too much money but the critical thing is to have a credible plan."

He said new taxes could be considered, pointing to Ireland's reform of property taxation during the financial crisis.

Lord Macpherson added: "Of course we have got to focus on the short term but the shadow of this crisis is potentially great and we need to ensure that the country gets through this with relatively sound public finances."

Former Labour chancellor Alistair Darling said comparisons between coronavirus and the financial crisis were "of limited value" as the government knew what it needed to do to fix the problem.

"The problem we face today is really quite different," he said. "We are clearly not on top of this problem."

Lord Darling said the UK would "always be on the back foot" until it catches up with testing for the virus – and said the government must be clearer on its programme for testing.

It comes after chancellor Rishi Sunak announced an unprecedented package of support for businesses and workers, including government-backed loans and a job retention scheme where the state will pay wages to prevent mass lay-offs.