He said that tricky growing conditions meant a slightly later start to the season than in previous years - with full supply established in the first week in May.
Sales of the vegetable reached £16.5m this season, with this year's market penetration figure standing at 12.4 per cent - the same as in 2006.
Hallett, who revealed the figures in London last week at a review of the 2008 PR campaign, said: "Demand for asparagus remained high this year but the crop needs sustained warmth and sunshine to thrive - both of which were in short supply in the second half of last year and throughout this season.
"Penetration and volume sales figures are not as healthy as they were in 2007, but last year we had a very good April, which brought the crop on early and encouraged consumers out to stores to buy a product that is intrinsically summery.
"We estimate that up to 40 per cent of asparagus sold in this year's season would have been imported to make up the shortfall created by last year's poor summer weather and this year's cold spring."
The good news is that the ongoing British Asparagus campaign - now in its sixth year and run by Pam Lloyd PR - generated £940,393 worth of print coverage, reaching an estimated 132 million readers.
In addition, web traffic to www.british-asparagus.co.uk increased, with more than double the number of visits in May 2008 than in May 2007, and over three times as many pages viewed.
"Quick & Easy!" was the central theme of the 2008 campaign, which focused on debunking the myth that asparagus is difficult to cook. Recipes were devised around the sub-theme of "how to impress in 10 minutes or less", and male audiences were targeted.