The US market was "littered with bodies of British suppliers who had failed", said Steve Dawson, president of Food from Britain North America.
Dawson told UK exhibitors at the 49th annual Fancy Food Show: "I can recall many suppliers confidently coming here and proclaiming that as Tesco had bought the product back in Britain, it must be successful in the US. That is not necessarily so. A keen understanding of distribution, labelling and market preferences is vital."
Distributors said British involvement in the war against Iraq had boosted sales of UK food and drink in the US. One said: "When Tony Blair came out in favour of George Bush's war declaration we saw a rise in demand for British products like Stilton, whisky and tea."