Zoella, Alexa Chung and other influencers pledge to make social media ads clearer

Singer Ellie Goulding, model Alexa Chung and vlogger Zoella are among those to volunteer to change their policies in the wake of a government investigation into the extent to which influencers are clearly and accurately identifying commercial relationships and whether audiences are being misled.

As a self-regulatory ad watchdog, the ASA governs how brands adhere to its guidelines about labeling such content. However, the CMA has the power to take legal action against people and all 16 celebrities who have pledged to change their ways were being investigated because they had broken trading rules.

In agreeing to be more explicit about paid-for content, the high-profile influencers have protected themselves against court action.

Each celebrity will be closely monitored by the CMA to ensure that they remain true to their word with the threat of court action, hefty fines and even a prison sentence of as much as two years for those who fail to clearly signpost ads.

Andrea Coscelli, chief executive of the CMA, said: "Influencers can have a huge impact on what their fans decide to buy. People could, quite rightly, feel misled if what they thought was a recommendation from someone they admired turns out to be a marketing ploy.

"You should be able to tell as soon as you look at a post if there is some form of payment or reward involved, so you can decide whether something is really worth spending your hard-earned money on."

The action follows on from the ASA saying it had warned "hundreds" of social influencers and brands to comply with its rules and stop posting opaque branded content.