Like most nations, the UK has different visa rules for nationals of various countries.
Citizens of the US, Canada, Australia, New Zealand and South Africa need a passport that is still valid for at least 6 months but do not need a visa to be allowed entry for 6 months as a tourist. They are not allowed to work.
Citizens of any of the European Union countries need a valid passport but not a visa to enter the UK, and are allowed to live and work here.
Citizens of Commonwealth countries, such as Australia, New Zealand, South Africa can apply for a working holiday visa that lasts for two years, but they must aged 17-30 when they first receive it. This visa must be obtained before arrival in the UK, Australians can get information on it at the Canberra British High Commission website and New Zealanders can check their High Commission site.
Visitors from other countries can go to the UKvisas webite run by the British Home Office and type in their nationality and country of residence to see the requirements for entry to the UK.
Going through UK Customs, there is a choice of three channels for travelers:
BLUE CHANNEL if you are travelling from an EU country with no banned or restricted goods and no tobacco products over the limit for imports from that country.
GREEN CHANNEL if you are travelling from a NON-EU country and have no more than the customs allowances and no banned or restricted goods.
RED CHANNEL if you have goods to declare or commercial goods, have tobacco products from an EU country that are over the limit for imports from that country or you’re not sure what you should declare.
The HM Revenue and Customs website lists what you are allowed to bring in from where.