|Too much: Channel 4 has been censured for sexualising a 15-year-old girl in this controversial poster|
The young blonde was heavily made up, her bra was showing and she was spilling out of a low cut top that revealed her breasts and cleavage.
The poster was one of a number that appeared under the slogan 'Bigger, Fatter, Gypsier' to advertise the second series of the fly-on-the-wall documentaries.
However, the Advertising Standards Authority (ASA) has ruled the broadcaster was 'irresponsible', while the image was likely to be harmful to the girl involved.
Complaints about a second poster of a 10-year-old boy with an aggressive expression were also upheld on the basis it stereotyped youngsters from the traveller community.
The decisions by the ASA are a victory for the Irish Traveller Movement in Britain (ITMB), which has accused Channel 4 of fuelling discrimination.
It welcomed the watchdog's ruling, saying it demonstrated that the way the broadcaster had portrayed the traveller community was 'morally bankrupt'.
Initially, the ASA refused to investigate the more than 300 complaints, however it only relented following an independent review.
The 'Big, Fat Gypsy Wedding' programmes have been a commercial and viewing success for Channel 4.
Channel 4 insisted the 15-year-old had chosen to dress as she did, while her outfit was in keeping with other girls and women at the party.
It said the image was a fair and accurate representation of one aspect of the Irish Traveller culture, while the girl had turned 16 before the posters were put up in February this year.
The broadcaster also insisted it had been given permission by the girl and her family to use the image.
However, the ASA, in a ruling published today, said: 'We noted that she was heavily made up, her bra was visible and that she was wearing a low cut top that revealed much of her cleavage and raised her breasts.'
The watchdog said: 'Although we understood that the girl was depicted in her own choice of dress we considered that, in choosing that image for use in a poster, Channel 4 had acted irresponsibly by depicting a child in a sexualised way.
'For that reason we also considered that, irrespective of any consent Channel 4 may have held, the ad was also likely to be harmful to the girl featured.'
It said the second poster showing the young boy with an aggressive expression was offensive and irresponsible because it fuelled a prejudiced view of travellers and so was likely to cause serious offence.
Chief executive of the ITMB group, Yvonne MacNamara, said: 'As a result of this decision, Channel 4's Big Fat Gypsy brand has been held up to be morally bankrupt.
'In its evidence to the ASA investigation, the Equalities and Human Rights Commission described anti-Gypsy and Traveller racism as the last respectable racism. The ASA has today made clear that it is no longer acceptable.