The UK economy could take until 2024 to return to the size it was before the coronavirus lockdown, according to analysis from the EY Item Club.
The forecasters, who use a similar economic model to the Treasury, suggest unemployment will rise to 9% from 3.9%.
They also estimate the economy will shrink by 11.5% this year, worse than the 8% they predicted only a month ago.
Consumers have been more cautious than expected, they said, while low business investment will dampen growth.
However, the forecasters say it is early days and useful data has only recently been made available.
“Unsurprisingly, without hard data, a wide range of views on the performance and outlook for the UK economy emerged,” said Mark Gregory, UK chief economist at EY.