An advert for the campaign group Hacked Off has been banned for misleading consumers with "ambiguous" information about Lord Justice Leveson's involvement in the Royal Charter.
The national press ad featured a number of names and the claim: "What do all these people have in common? The Leveson Royal Charter Declaration."
It said: "More than a year on from the Leveson Report, leading figures in literature, arts, science and the law are joining with victims of past press abuse to say: We believe that a free press is a cornerstone of democracy."
It continued: "We also believe that editors and journalists will rise in public esteem when they accept a form of self-regulation that is independently audited on the lines recommended by Lord Justice Leveson and laid down in the Royal Charter of 30 October 2013."
A complainant said the advert, and particularly the title of the declaration, misleadingly suggested that the Royal Charter and all of its contents had been proposed, recommended, written or endorsed by Lord Justice Leveson.
Hacked Off said there were many royal charters and that it believed the ad would have been unclear if the word 'Leveson' had been omitted.
The group said it believed the declaration itself "made absolutely clear" that it was about a specific royal charter "on the lines" recommended by Lord Justice Leveson.
But it added that the charter itself was an instrument disseminated by Government with Parliamentary endorsement, and that on the Government's own website it was referred to as 'Leveson Report: Cross Party Royal Charter'.
The Government passed a Royal Charter last year in the wake of the Leveson Inquiry into press standards, intended to underpin a new press watchdog.
However, the process has not won industry backing and a number of newspapers have established an Independent Press Standards Organisation that does not have the backing of the charter.
The Advertising Standards Authority (ASA) said consumers would be aware that Lord Justice Leveson had made a number of recommendations as a result of the inquiry findings.
It also said consumers would be aware that there was a movement towards the establishment of a new model of press self-regulation as a direct result of the recommendations, but it was not so well known how this would be implemented.
The ASA said: "We therefore considered that, without a clear qualification, consumers would understand the title 'The Leveson Royal Charter Declaration' to be a claim that the Royal Charter to which the declaration related was one of the direct outcomes of the Leveson public inquiry, rather than a response to it."
It also found that the "strong suggestion" of Lord Justice Leveson's involvement in the charter alongside a conflicting statement regarding the indirect influence of his public inquiry recommendations "provided consumers with confusing and ambiguous statements regarding the nature of any involvement of Leveson in the Royal Charter".
"As a result of this ambiguous information, we concluded that the ad was likely to mislead," it said.
It ruled that the ad should not appear again in its current form, adding: "We told Hacked Off to ensure future ads made clear that Leveson had not proposed, recommended, written or endorsed the Royal Charter."
Hacked Off said in a statement: “We are disappointed in the ASA ruling, and particularly disappointed that, unusually, the Council has chosen twice to overrule the decision of its own professional staff on this advert, which first appeared over a year ago, and has not been re-used for 9 months. It will therefore strike many as a political judgement, made by a body part-funded and appointed by the press industry and we will be appealing the decision.
"We believe that the advert promoting the Royal Charter was very clear in what it was aiming to achieve and was not misleading. This was accepted by the ASA’s professional staff back in April when they originally threw out the complaint and then again in November in their recommendation to the Council.
"The public, Hacked Off and the press industry all accept that the Royal Charter implements the Leveson Report recommendations – as our Declaration makes clear. It is only the ASA Council, still fighting last year’s war, which thinks otherwise.
"Hacked Off will of course abide by the ruling of the ASA, pending the appeal process."