The central scenario saw 2020 output falling by 12.4%, with the jobless rate peaking at 11.4%. It currently stands at 3.9%.
Last month UK debt passed 100% of GDP for the first time since 1963 and the government broke records for monthly borrowing.
The OBR said that while the government was rightly focused on limiting the damage of the pandemic, it would eventually have to tackle the sky-high debt and budget deficits.
“It seems likely that there will be a need to raise tax revenues and/or reduce spending (as a share of national income) to put the public finances on a sustainable path,” the OBR said.
The OBR was set up by former Chancellor George Osborne in 2010 to provide an independent audit of public finances, with a focus on the sustainability and affordability of debt.