It's run on a broad understanding of "passing off". If one brand may be confused with the other, or mistakenly be associated with, or get the benefits of the image of it, the action may get home.
This has amusing consequences sometimes. When Mr Borwick junior, started a baking powder business under his name, he was sued by his father. Borwick's baking powder was a famous brand, owned by Borwick senior. The son's defence was that he was only use his own name. The court was not impressed, particularly when it discovered that the packaging was the same colour. Mr Albert Hall, a bandleader, called his band 'The Albert Hall Orchestra' He was stopped by the trustees of the Royal Albert Hall.
And some are just odd. The World Wrestling Federation, the WWF, won a case against the World Wildlife Fund, the WWF, although the connection between pandas or wild beasts on the verge of extinction and wrestlers was not clear. Although, on second thoughts....