Dust from the Eyjafjallajokull Volcano in southern Iceland has closed airports across much of Europe and canceled most trans-Atlantic travel.
The Daily Telegraph reported the stock for clothing retailers is sitting in holding pens overseas waiting to be flown to Britain.
Air freight accounts for 25 percent of the country's movement of international goods.
The Freight Transport Association said the cost to business and consumers will rise.
Grant Liddell, retail director of Uniserve Group, the British private logistics provider, said: "Even when airspace opens up we are looking at a backlog. It will take 48 hours to sort out as a lot of carriers now have their aircraft mispositioned across the globe. Where clothing is concerned it could take two weeks to clear the backlog."
The problem does not extend to groceries. A spokesman for Tesco, the retail grocery chain, told the newspaper: "Less than 1 percent of what we sell comes into the U.K. via air. At the moment there is no impact and we have enough stock. We are keeping a very close eye in it at the moment."
A spokesman for the British supermarket chain Asda told The Daily Telegraph: "We don't have much of a problem. Where we do import fruit by air it tends to be exotic fruit. We have a good stock at the moment."