From the Advertising Standards Authority;

Advertisers and promoters bear principal responsibility for the advertisements and promotions they produce and must be able to prove the truth of their claims to ASA: they have a duty to make their claims fair and honest and to avoid causing offence. Advertising agencies have an
obligation to create advertisements that are accurate, ethical and do not mislead or offend. Publishers and media owners recognize that they should disseminate only those advertisements that conform to the Code. They accept the rulings of ASA Committee as binding.