Trade marks are the strongest form of protection available for UK business names and supersede company registrations. When you register a company name the government do not check to see if it conflicts with an existing trade mark. If it does you can be forced to change the name of your company and ditch any branding you may have done around your business.
All UK trade marks are registered with the Intellectual Property Office (IPO). There are 45 different trade mark classes which cover different business activities. A trade mark can be registered in one or more classes at a time. It is possible for different businesses to get trade marks on the same words or phrases as long as they are in different classes. So, for instance, Volkswagen have trade marks registered in classes 04 07 12 27 28 37 for the word Polo to cover the model of car they make while Nestle have a trade mark for Polo under class 30 to cover the mints. Because the two products are in different classes they can both have a trade mark on the same name.
As well as getting a trade mark on a business or product name it is possible to register a trade mark on a logo. One of the most common reasons for trade mark applications being rejected is where a business name is not unique enough or being to general. In these cases it is often still possible to get some protection by getting a trade mark on the logo design which contains the business name.