Starbucks took issue with the headline claims in the posters – that “7 out of 10 Coffee Lovers Prefer Costa” and “Starbucks Drinkers Prefer Costa” – calling them misleading because of alleged faults with the research.

In an adjudication published this morning the ASA dismissed the complaint, citing its own expert’s view that the survey methodology “did not contain design errors, that the results were statistically significant and the sample size was adequate”.

The research, conducted by Tangible, involved 174 self-described coffee lovers taking part in a single blind taste test, which the ASA deemed “acceptable”. In the research, 70%of participants expressed a preference for Costa’s cappuccino over that offered by Starbucks and Caffe Nero.

A separate survey, pitting Costa against only Starbucks, involved 166 people – 57 of whom identified themselves as Starbucks drinkers. Of those Starbucks drinkers, 67% said they preferred Costa’s cappuccino.

In its decision, the ASA noted there were “weaknesses in the amount of reported detail on the methods used” in the research, and that “consequently some of the information provided about the methodology had to be taken on trust”.

However, the ASA did not find Costa’s ads in breach of various clauses in the advertising code relating to substantiation, truthfulness and comparisons with competitors.

Costa marketing director Jim Slater welcomed the adjudication. “The ASA has run an extremely through investigation, which has found Starbuck’s complaints to be without merit.”

Starbucks had previously complained to Ofcom about the ads when broadcast in radio form. That complaint, made against broadcaster Bauer Radio, was upheld for failing to provide appropriate qualification to the claims made in the campaign.