Perviously the ASA scrutinised television, radio and print media but announced last September that websites and social networking sites like Twitter and Facebook would also come under its remit.
The move was prompted by the fact it had received 4500 complaints about online marketing since 2008 which it had not been able to investigate.
“This landmark development addresses a regulatory gap online,” the ASA said.
“The Non-broadcast Advertising Code will apply in full to UK based companies’ websites, including the rules relating to misleading advertising, social responsibility and the protection of children. The remit will apply to all sectors and all businesses and organisations regardless of size.”