The high street favourite pipped Boots, Amazon, Lego and Dyson to take the top spot, in an authenticity study of 15,000 people worldwide carried out by Cohn & Wolfe.
Consumers were asked to rank the list of attributes in order of importance to them, with data protection ranked as their top concern.
This makes the handling of personal data doubly significant for brands, given stringent new rules on data protection set to come into force next May under the General Data Protection Regulation. Under the new rules, companies and organisations which mishandle people’s personal data could face significant fines, as well as censure from the Information Commissioner’s Office.
Additional measures by which consumers judged the authenticity of the brands in the study included treating customers well, delivering on promises and communicating honestly.
Scored out of 100 against public perception of these attributes, Marks & Spencer, which took the second spot last year's study, received 92.33 points, with Boots on 89.65 and Amazon on 88.53.
The study found Amazon to be the most authentic brand globally, with Apple, Microsoft, Google and Paypal making up the top five.
In the UK, social media sites in the study received poor scores against the technology sector average of 58.85, with Facebook the highest scoring on 52.55 points, while Twitter scored 39.22.
Scott Wilson, chief executive of Cohn & Wolfe UK, said: "If people are convinced that you are authentic, our research shows they are more likely to listen, or purchase. Beyond that, they are more likely to recommend your brand to others – and to stick with you during times of crisis."
He added: "This shows that authenticity is a key driver of reputation. And to be authentic, a brand must be reliable, respectful and real. Brands should consider how authentic they are and what they can do to be more authentic – the business benefits will be very real."