Carling has insisted that customers have not been misled, after conceding that the actual level of alcohol in its beer it lower than the amount advertised.
Carling advertisers the lager as having 4% alcohol by volume (ABV) but it has been brewed at 3.7% since 2012.
The admission from the brewery's US-based owner, Molson Coors, came during a hearing brought by HMCR which centered around claims that Carling had underpaid tax by more than £50m between September 2012 and January 2015.
However, the firm won the case in March this year after arguing that the actual strength of its lager meant it shouldn't be subject to the higher taxes owed on products with more than 4% ABV.
According to EU laws on alcohol packaging, beer products are allowed to have a a natural variation of 0.5% and as such there is no suggestion that Carling has broken any laws.
Molson Coors said in a statement: "As a major brand, the trust of our consumers is paramount. We abide by all legal requirements in the brewing and labelling of Carling.
"The natural process of brewing means all batches of Carling vary fractionally in alcohol content - the variation range for Carling is less than a quarter of 1% (0.23%).
"It is completely normal for consumable products to have a slight variation. For example, the allowed variation for wine is 1%."
Earlier this year, the brand modernised its packaging design to ensure a "single-minded consistency" across its entire portfolio, which includes lager and cider, as well as fruit flavoured and premium alternatives.