One promotion - in an Asda in Brighton - sees 20x44cl cases of Carlsberg at three-for-£20, or 75p per litre. That is well below last year's lowest price of 91p/litre in an OLN survey, and a "significant discount" on prices wholesalers pay, according to Steve Parfett of wholesaler AG Parfett.
"It gives a facade of legitimacy to the sort of prices duty fraudsters offer, which would otherwise look as ridiculous as they clearly are," he warned.
"This cannot be good for the market, particularly with the emphasis on the irresponsible nature of promotions. The supplier and the multiple have a joint responsibility to do something about it."
A Carlsberg spokeswoman said pricing is up to retailers.
Asda also has a two-for-£18 and three-for-£24 promotion on £10 cases of a number of beer and cider brands, while Tesco online has been running short-term two-for-£16 and three-for-£20 offers on various 18x44cl cases - 84p/litre if customers buy three. Sainsbury's online has three-for-two promotions on £10 packs of Carlsberg and Stella Artois.
The Co-op has been promoting a range of lager cases at £9.99, Thresher is running promotions on smaller packs, and Bargain Booze has ongoing discounts.