If you are not a British citizen, you will need an entry permit to go to the UK. The Home Office has three categories to grant the entrance fee:
European Economic Area Citizens , Citizens of the European Economic Area: Do not need permission to enter the Kingdom. Including all EU countries, Norway, Liechtenstein and Iceland. Citizens of the Swiss Confederation are also included in this category.
Non-Visa Nationals : Need an entry certificate to go to the UK to work or settle. This category is mainly made up of Commonwealth citizens.
Visa Nationals : Need a Visa to enter the UK for any reason.
You will also need a visa if you; (i) Do not have a nationality ( stateless ), or (ii) have a document that does not give you the nationality or citizenship of the country that gave it to you (example: a driving license), or (iii) possess a passport that is not recognized in the United Kingdom.
UK visit visas are issued for a maximum period of 6 months. If you wish to stay longer, you will have to leave the country and ask for a new visa. If you want to go to the UK freely, you will need to apply for a multiple-entry visa , otherwise you will have a single-entry visa that will allow you to enter only once in the UK.
Following are the four main visa categories for which most of the visa applications are made for the UK: