Britain's economy was set to grow by 2.2 per cent this year and next, matching official gross domestic product for 2015, the International Monetary Fund said.
But it warned that "uncertainty associated with the outcome of the forthcoming referendum on EU membership could also weigh on the outlook" along with various other factors including "potential shocks to global growth and asset prices".
As Britain prepares for a June 23 referendum on its EU future, British Prime Minister David Cameron has warned that the country's departure from the European Union would threaten its economic and national security.
"Quantifying how a decision to leave the EU would affect the economy is difficult, given that the terms of staying in the EU are still being negotiated and the nature of post-exit relations with the EU are unknown," the IMF said in its latest outlook for Britain.
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"However, analysts have raised concerns that the exit debate could bring a period of uncertainty that could weigh on investment," it added.
Almost 200 bosses of top British companies yesterday urged voters to keep Britain in the European Union, warning that an exit from the 28-nation bloc would threaten jobs.
Sterling meanwhile today fell below USD 1.40 to a seven-year low on growing worries that Britain may vote to leave the European Union.
Britain's currency has been hit in recent times also by increased expectations that the Bank of England may wait until at least next year to raise interest rates amid weakening growth at home and abroad, according to analysts.