The watchdog ruled that Cadbury's Trident TV and cinema ads, created by JWT, breached the broadcast TV advertising standards governing offence and ethnic stereotyping.
The Advertising Standards Authority found that the four Trident ads did not incite racial intolerance, but could be seen as belittling to black or Caribbean people.
The first ad, which invokes the spirit of "revolutionary poets", featured a West Indian dub poet on stage talking about the blandness of chewing gum. An audience member hands him an exciting new type of gum, which prompts him to launch into a journey that takes him onto a boat sailing past the Houses of Parliament, shouting "mastication for the nation" through a megaphone.
The ad has become one of the most complained about of the year, racking up 519 complaints. The ASA said that greater sensitivity was required of advertisers using humour based on accents, because of the "potential to cause serious offence" and in particular if it could be seen to be patronising or demeaning to groups of people who suffer racial prejudice.
The ASA said: "The stereotype depicted in the ads had, unintentionally, caused deep offence to a significant minority of viewers and that many of those who complained to use were concerned that the negative stereotype could be perpetuated."
However, the watchdog rejected complaints about the Trident brand name. Viewers claimed that it was offensive because Trident is also the name used by the Metropolitan Police initiative to tackle black gun crime in London. It was not believed that there were complaints made about Trident also being the name of the UK's nuclear deterrent.
Cadbury defended the £10m campaign, saying that it was meant to depict a "humorous and tongue-in-cheek gum revolution". The confectionery manufacturer said it had sought the views of members of the Afro-Caribbean community and the general public during the campaign's development. Only a few had found the ads offensive, while two thirds had found them funny, Cadbury said.
Trident is not the only campaign to fall foul of the TV viewing public this year. The Department of Health's anti-smoking "fishhook" campaign has notched up 769 complaints so far, winning it the number eight spot in the most complained-about-ads rundown.
Topping the list with 1,600 complaints was KFC's TV ad featuring call-centre workers singing with their mouths full. Created by Bartle Bogle Hegarty in 2005, the ad drew the wrath of parents for encouraging bad table manners.