The government will unveil its first Budget later amid continued pressure from the coronavirus outbreak.
The new Chancellor, Rishi Sunak, will present the fiscal plans in the Commons at 12:30 GMT, less than a month after taking over the Treasury.
Some elements have already been revealed, including more than £600bn for infrastructure projects over five years and extra money for potholes.
But the economic challenge posed by the virus is still expected to dominate.
The number of coronavirus cases in the UK reached 382 on Tuesday, a rise of 63 since the previous day, with a sixth person confirmed to have died from the virus.
Mr Sunak has said the NHS will get “whatever resources it needs” during the crisis and that he is looking at extra financial help for individuals and businesses who are left out of pocket.
The Budget also comes in a week in which shares around the world – already hit by fears about coronavirus – suffered some of their biggest falls since the 2008 financial crisis.
Dubbed “Black Monday”, indexes tumbled as a row between Russia and Saudi Arabia saw oil prices plunge, with declines in London wiping some £125bn off the value of major UK firms.
On the eve of the Budget announcements, the Treasury pledged to triple the average net investment made over the last 40 years into rail and road, affordable housing, broadband and research.
It said this would lead to the “highest levels [of investment] in real terms since 1955” – more than £600bn over the five-year Parliament – and be targeted “in every region and nation of the UK”.
Mr Sunak said: “We have listened and will now deliver on our promise to level up the UK, ensuring everyone has the same chances and opportunities in life, wherever they live.
“By investing historic amounts in British innovation and world-class infrastructure, we will rebalance opportunities and lay the foundations for a decade of growth for everybody.”
But shadow chancellor John McDonnell called the figures “exaggerated claims”, adding: “Boris Johnson has a track record of boastful claims followed by non delivery and it looks like he is running true to form.”
BBC political editor Laura Kuenssberg said the decision marked a significant increase in the amount of spending on capital projects compared with the period since Margaret Thatcher came to power in 1979.
However, she said it was not yet clear whether the government would stick to its own fiscal rules set out in its manifesto.
The government is also set to pledge £2.5bn to fixing potholes in England as part of the Budget.
The Treasury said the money would also be available to local authorities to start resurfacing works, preventing potholes from appearing in the first place.
But Mr McDonnell said the policy was part of a “gimmicky grab-bag of projects”.
Wednesday’s Budget will also be the first time a woman has chaired the proceedings in the Commons’ history.
Dame Eleanor Laing was elected as the House’s first woman chairman of ways and means in January – the most senior deputy speaker – who traditionally oversees the Budget.
She said she “probably will be a bit nervous” on the day, but said, with a new chancellor in post as well, “we will all be newbies”.