An unprecedented level of butter and spread promotions is eroding customer loyalty, brand owners have warned.

The percentage of products sold on deal in butters and spreads has rocketed from 26% in the three months to 19 April 2008 to 43% in the same period this year [Nielsen 12w/e 18 April], while the number of paid-for off-fixture promotions was up 143% in the year to May [Assosia].

"There has been more switching between brands than ever before," said Stuart Ibberson, group brand manager at Arla Foods, which produces Anchor and Lurpak. "Promotions are eroding loyalty, as people are tempted by brands they wouldn't normally try."

Only price increases prevented the deluge of deals causing a fall in the value of the market, which rose 10.9% to £1.15bn, he said. "If prices hadn't risen so significantly last year but the level of promotions had remained, we would have seen value going the other way," he said.

Meanwhile, own label has lost two percentage points from its share of the market this year, as promotions allowed brands to undercut own-label prices.