The statement comes in response to controversy in India over the company Speak Asia, which has taken out TV ads promising respondents handsome returns for joining its research panel and referring others to do so – but only after they pay a substantial fee.

Ram Survey, which claims to be India’s largest survey company, advertises a similar business model, with the promise of huge potential returns for referring others to join the panel.

Esomar denounced such practices as unethical, misleading and in breach of the “key fundamentals” of its code.

The association’s director general Finn Raben said: “Respondents should never be expected to pay for participating in a survey and this practice is highly damaging to the image of market research.”

“Market research depends on public confidence that it is carried out honestly, objectively and without disadvantage to its participants,” said Raben. “A key tenet of the ICC/Esomar International Code is that market researchers shall behave ethically and not abuse the trust of respondents or exploit their lack of experience or knowledge. People participate for all sorts of reasons, not least because they want to share their thoughts about the products and services they use and how they would like them to be improved. Whilst they may receive small incentives for giving up their free time to answer a questionnaire, it is unheard of that respondents should pay to participate in research.”

No responsible market research company would require this, Raben said, and if any Esomar member were to be found doing so, they would immediately be expelled.

The Market Research Society of India joined Esomar in condeming the practice, saying that none of its members ask respondents for payment to take part in any of the surveys they conduct.

Speak Asia is now being investigated by the Indian authorities. The company, whose offices are in Singapore, was not available for comment at the time of publication. Ram Survey had not responded to an email seeking comment.