The International Monetary Fund has warned about the "uncertainty" caused to the UK economy by David Cameron's plans for an in/out referendum on European Union membership.
IMF managing director Christine Lagarde also hinted that the vote should be held sooner rather than later.
The IMF chief said "certainty is always better than uncertainty" when asked about the prospect of waiting up to two years for a vote on a possible British exit.
She stressed that in her personal view she hoped that the UK would vote to remain in the 28-member bloc.
The next report by IMF inspectors will be produced in May 2016 and will examine the potential consequences of a British exit from the EU, Ms Lagarde said.
The issue was identified in the annual health check by the IMF on the UK's economy, which also highlighted concerns about high house prices, the UK's current account deficit and the public finances.
But it was a broadly positive assessment, which stated "the UK's recent economic performance has been strong, and considerable progress has been achieved in addressing underlying vulnerabilities".
Chancellor George Osborne said: "Today's IMF report, frankly, could hardly be more positive."
Forecasts produced by the IMF suggested "steady growth looks likely to continue over the next few years", averaging around 2.25% in the medium term.
Asked about the prospect of a referendum being delayed until the end of 2017 deadline set by the Prime Minister, Ms Lagarde said: "Certainty is always better than uncertainty, that's a commonplace statement on the part of the IMF".
"But as an economist and in charge of doing forecasts, I'm trying to assess and model through the various hypotheticals, the more certainty we have, the better," Ms Lagarde said.
She said there was little sign of economic damage from the referendum yet, but there were key measures which could give an indication that the uncertainty was deterring investors.
"I think what will be interesting to watch is to look at the balance of payments, to look at how much foreign direct investment is coming in, to look at the borrowing pattern of the UK, how are the Treasury bond issuances over-subscribed?
"If there is a sense of disenchantment or concern, as observed in the future - because we are not seeing it at the moment - then it would be an indication that certainty would be much better than uncertainty."
She said at the moment the IMF was underlining that there is uncertainty, which is "not terribly helpful" but would examine the alternatives to British EU membership in its next report in May, which could come just weeks before the referendum if Mr Cameron chooses to hold it in June as he has reportedly considered.
Among factors that needed to be considered were: "How quickly will there be trade agreements? How promptly will the partners want to re-establish or reset the framework within which both financial and trade relationships are put in place?"
At the launch of the IMF's report in the Treasury, Ms Lagarde praised the UK's response to the global financial crisis.
"The UK authorities have managed to repair the damage of the crisis like very few other countries have managed," she said.
"We are saluting a very strong performance by the UK economy," she stated.
The IMF chief said there had been indications of a "slight improvement" in the UK's historically poor productivity levels.
But she expressed concerns about the housing market, even though prices were not rising as fast as they had.
"House prices are still growing faster and higher than income grows," she said.
"In addition, while household debt has stabilised, it has stabilised at fairly high levels. That leaves small households vulnerable to income and interest rate shocks."
The IMF said tightened loan-to-income limits or the imposition of loan-to-value caps could be needed if the amount of higher-leverage mortgages do not continue to fall.
The Financial Policy Committee's remit on mortgage lending should also be extended to cover buy-to-let loans, the IMF recommended.
