Downing Street has failed to quash reports that taxes could be hiked or public sector workers have their pay frozen to pay for the fallout of coronavirus.
According to a leaked Treasury plan, nurses, doctors and firefighters could be among those clobbered as the Government tries to repair the economy.
The document - obtained by the Telegraph - listed a string of options ministers could take to tackle a budget deficit as high as £337bn this year.
While none of them are government policy, the document suggested the "tax lock" promised in December's election - freezing Income Tax, VAT and National Insurance - could have to be scrapped.
It also suggested a two-year public sector pay freeze could save £6.5billion by 2023-24 - while "stopping the rising cost" of the pension triple lock would cut £8billion a year.
The Prime Minister's press secretary today emphasised Boris Johnson recognises the work of frontline workers and "we're not going to forget that".
Pointing out the PM has already promised no return to the days of austerity, he added: "We are determined to support them."
However, he was unable to categorically rule out either a pay freeze or tax increases - saying a future Budget had not yet been written.
Most public sector workers have suffered almost a decade without an above-inflation pay increase as part of Tories' austerity agenda.
Unions say the public will not tolerate a move to make frontline heroes in the Covid-19 crisis foot the bill.
The assessment, drawn up for Chancellor Rishi Sunak and dated May 5, warned that to plug a gaping hole in the public coffers through tax rises would be "very challenging without breaking the tax lock".
Measures including income tax hikes, a two-year public sector pay freeze and the end of the triple lock on pensions were mooted in the document to fund the debt.
Today the Prime Minister's press secretary paid tribute to frontline workers but could not categorically rule out a pay freeze.
He said: "We acknowledge that those on the frontline are doing an incredible job at the moment and we are determined to support them.
"Public sector pay decisions are made through the usual annual process and recommendations from the review bodies will be considered before pay awards are announced this summer.
"I would also say that we obviously recognise the work of the frontline staff in the current crisis and we're not going to forget that after we're through this crisis."
Asked a second time if he could rule out a pay freeze for frontline workers he said: "I just answered that and don't have anything to add to that."
Asked if the PM would stick to the tax lock made in the 2019 manifesto, his Press Secretary instead pointed to the March Budget.
He said: “The Chancellor was asked about this this morning and he said we remain committed to the agenda that was set out in the Budget and that is about spreading opportunity, investing in infrastructure as that is how you drive growth and, at the same time, support our public services."
And asked if the pensions triple lock - which guarantees generous yearly increases for OAPs - still stands, he said: "It's too early to speculate about any future decisions.
"We're facing a time of unprecedented economic uncertainty and we remain committed to the agenda that was set out in the Budget."
He confirmed that Boris Johnson remains opposed to bringing back the austerity agenda.
But union chiefs have warned about the damage of such a strategy.
Dame Donna Kinnair, general secretary of the Royal College of Nursing, said that the public would be "outraged" if nurses were to bear the brunt of this policy.
She said: "This proposal is the exact opposite of what's expected and deserved and, if pursued, will outrage professionals and public alike.
"We will make sure no government forgets the professionalism demonstrated by all nursing staff during this pandemic and before it."
Unison general secretary Dave Prentis said: "It's appalling that anyone in the Government is even contemplating freezing public sector pay. The public will be horrified by these cheap tactics.
"Throughout the lockdown, NHS, care, council, police and school staff have kept services running, saving lives, caring for the vulnerable and ensuring our communities are safe.
"Public service workers deserve proper recognition for these efforts and the Government should work with unions and employers to agree a handsome pay rise. Anything less would be a slap in the face to all of those we applaud each week."
Harry Quilter-Pinner, of the IPPR think tank, said: "Public sector workers, from nurses to teachers, have been the heroes of the Covid-19 pandemic. Their service to our country must be rewarded with a pay rise, not taken for granted with a pay freeze. We cannot return to the dark days of austerity."
