Philip Hammond is facing a yawning £84bn shortfall in public finances over the next five years, according to policy experts.
The chancellor is set to make his first Autumn Statement in just under a month, but sums from the Resolution Foundation suggest Treasury coffers are going to be under intense pressure thanks to economic turbulence.
The think tank adds that hopes of a surplus by 2020 have also been shattered, with a £13bn deficit likely.
The Resolution Foundation modelled the figures on the average change in forecasts from March 2016 to the latest projections from the Office for Budget Responsibility, published after the latest borrowing figures came in significantly worse than economists had expected.
It welcomed Hammond's recent comments around a “fiscal reset” but adds the chancellor should either soften his deficit target for 2019-20, or delay it by an extra year in order to respond to deterioration in the economy.
“The good news for Philip Hammond is that by softening his fiscal target he has significant political and economic room for manoeuvre,” Resolution Foundation chief economist Matt Whittaker said.
“But the trade-off for this approach is significantly higher borrowing in the coming years. The chancellor will need to decide if that is a price he is prepared to pay for adjusting to new economic times and setting out a direction for the new government.”
However, Legatum Institute director of economy policy Shanker Singham said that uncertainty around the UK's future in the aftermath of the summer's Brexit vote make reliable forecasting impossible.
“If it leads in a positive direction then we could see quite a lot of growth and productivity increasing in the UK which these models to do not take into account,” he said.
“Numbers like this aren't very useful number because when there is so much uncertainty.”