The advert was banned in January after the Advertising Standards Authority received two complaints that the image used was "overly sexualised" and objectified women.

But this week, it said the decision had been reviewed due to "our concern that our rationale for banning the ad was substantially flawed".

"After careful thought, our council, the independent jury that decides whether UK ads break the rules, considers that the image was not sexually explicit, that the ad presented FKA twigs as confident and in control and, therefore, that she had not been objectified."

The British musician, 36, had been featured on the poster wearing a denim shirt that was drawn halfway around her body, leaving the side of her buttocks and half of one breast exposed, with text reading: "Calvins or nothing."

After the advert was banned, FKA twigs, whose real name is Tahliah Debrett Barnett, had been among those criticising the decision, saying: "I do not see the 'stereotypical sexual object' that they have labelled me.

"I see a beautiful strong woman of colour whose incredible body has overcome more pain than you can imagine.

"In light of reviewing other campaigns past and current of this nature, I can't help but feel there are some double standards here."

Calvin Klein also defended the ad, saying FKA twigs was a "confident and empowered woman" who approved the image before publication.

Following the original ruling, the ASA's director of complaints and investigations, Miles Lockwood, said the watchdog found itself "damned if we do, damned if we don't" in such situations, saying: "This is a clunking great big poster on the street in an untargeted medium. Children are seeing it alongside adults, and sometimes that gets missed.

"We are balancing the right of the advertiser's freedom of expression with protecting the public from offence and harm, and that's the process we go through every week."