Sunak has already racked up Britain's highest borrowing since World War Two and he will turn to the bond markets again in his budget speech, saying the task of fixing the public finances will only begin once a recovery is in sight.
He is expected to tell MPs: "First, we will continue doing whatever it takes to support the British people and businesses through this moment of crisis". It shrank by 10% past year, its worst slump in three centuries.
The Chancellor is promising to use the "fiscal firepower" of the government in his Budget tomorrow to get Britain's economy back on track.
Their contribution will increase to 20% in August and September, as the economy reopens, but employees will continue to receive 80% of their salary for hours not worked until the scheme ends.
The Coronavirus Job Retention Scheme (CJRS) had been due to expire at the end of April, raising fears of a sharp jump in unemployment at a time when the economy is still likely to be struggling under the weight of coronavirus restrictions.
The government on Saturday said Sunak will announce £5 billion of additional grants to help businesses hit hard by pandemic lockdowns, in his budget.
"Along with a wealth tax and inheritance tax I suspect that will be put in the "too difficult" box at this Budget" he says. "You are looking at catastrophe relief".
In a series of announcements ahead of his set-piece speech, Mr Sunak said the United Kingdom will launch a sovereign green savings bond for retail investors to help cut greenhouse emissions to net zero by 2050.
Sunak has said he will be "honest" about the cost of the unprecedented support and has pointed to borrowing costs rising from record lows recently, sparked by the prospects of a global economic recovery and U.S. President Joe Biden's almost $2 trillion stimulus plan.
UK Chancellor of the Exchequer Rishi Sunak will present his Budget to the Westminster Parliament later Wednesday but with numerous measures pre-announced it is unlikely to roil either GBP or the UK stock market.
But he is expected also to increase corporation tax, or a levy on company profits, from a United Kingdom record-low 19 percent while sticking to the Conservative government's pre-pandemic pledge not to increase income tax or value added tax (VAT).