The UK economy will perform worse than every other major country in 2023, according to the International Monetary Fund.
Even Russia - hit by swingeing economic sanctions by the global community due to its invasion of Ukraine - will out-perform Britain, the IMF said.
The forecast by the highly-respected body comes on the third anniversary of Brexit.
In its latest World Economic Outlook update, the IMF predicted the UK economy will shrink by 0.6% in 2023, compared to its October prediction that it would grow by 0.3%.
By contrast, every other country in the G7 group of advanced nations will see their economy grow - with America’s set to expand by 1.4%.
Russia’s economy will grow by 0.3% over the next 12 months, the IMF said.
Among the other G7 nations, the IMF’s 2023 predictions show growth, 0.1% in Germany, 0.7% in France, 0.6% in Italy, 1.8% in Japan and 1.5% in Canada.
China’s economy will grow by 5.2%, the IMF said, with India’s expanding by 6.1%.
Overall, the IMF said the global economy will grow by 2.9%.
The grim findings come against a backdrop of public sector strikes over pay and predictions that the UK is heading for a recession, with inflation still standing at more than 10%.
The IMF said Britain’s predicted GDP fall reflects “tighter fiscal and monetary policies and financial conditions and still-high energy retail prices weighing on household budgets”.
The forecast is yet another blow for Rishi Sunak, whose government is already facing multiple problems just three months after he became prime minister.
In an attempt to put a positive gloss on the IMF forecast, chancellor Jeremy Hunt said: “The governor of the Bank of England recently said that any UK recession this year is likely to be shallower than previously predicted, however these figures confirm we are not immune to the pressures hitting nearly all advanced economies.
“Short-term challenges should not obscure our long-term prospects – the UK outperformed many forecasts last year, and if we stick to our plan to halve inflation, the UK is still predicted to grow faster than Germany and Japan over the coming years.”
But shadow chancellor Rachel Reeves said: “Britain has huge potential - but too many signs are pointing towards really difficult times for our economy, leaving us lagging behind our peers.
“The government should be doing all it can to make our economy stronger and to get it growing.
“It is the only way that we can move beyond lurching from crisis to crisis as we have been for far too long.”