The UK has established a generic visitor visa system covering the categories of family and business visit, sports and entertainment visas.
The maximum period a visitor can stay in the country is six months.
Some countries are exempt from applying through a British consulate and are able to apply for a visa at the airport upon arrival in the UK, as is the case for Brazilian visitors.
However, if you want to ensure that your entry is guaranteed, the best option is to apply for a tourist visa in advance through the British Consulate in your country.