Retailers should steer clear of the "crude instrument" of bogofs and price discounting on berries - or risk devaluing the category, a leading consumer trends analyst has warned.

The value of the berry sector had been driven up by larger punnet sizes, a wider choice of packs, and new premium lines that had persuaded shoppers to trade up, Andrew Fearne, researcher at the Dunnhumby Academy, told the Global Berry Congress.

He called on retailers not to undermine higher prices and margins by introducing bogofs to a category that had avoided them to date.

"The berry sector has so much going for it and the retail berry market continues to ride the crest of a wave," he said. "It can address all the key consumer issues of provenance, health and taste. Price promotions are a crude instrument that don't build long-term sales."

Retail sales of strawberries alone are up 16% in the year to 20 January, according to Dunnhumby.

"The value strawberry proposition may have brought in more shoppers but higher-value lines such as Kentish strawberries have brought in more revenue and consumers are trading up," he said.

Other new premium strawberry varieties such as Ava and Jubilee were also proving popular with consumers as breeders researched ways of generating further value.

Retailers should also continue the recent trend for using larger packs, which were higher-priced and brought greater margins, Fearne said. This would enable them to grow the category, sell more fruit and pass more back to growers.

Meanwhile sales of blueberries and blackberries were rising rapidly, Fearne added, though raspberries were "struggling to keep pace".

UK blueberry sales could even soon overtake those of raspberries, according to Angus Soft Fruits' MD Lochy Porter.