The following may enter the UK without a visa for up 6 months; Andorra, Anguilla, Antigua and Barbuda, Argentina, Aruba, Australia, Austria, Bahamas, Barbados, Belgium, Belize, Bermuda, Botswana, Brazil, Brunei, Bulgaria, Canada, Chile, Costa Rica, Croatia, Curacao, Cyprus, Czech, Denmark, Dominica, El Salvador, Finland, France, Germany, Greece, Grenada, Guatemala, Honduras, Hong Kong, Hungary, Iceland, Ireland, Israel, Italy, Japan, Kiribati, Latvia, Liechtenstein, Lithuania, Luxembourg, Macao, Malaysia, Maldives, Malta, Marshall Islands, Mauritius, Mexico, Micronesia, Monaco, Namibia, Nauru, Netherlands, New Zealand, Nicaragua, Norway, Palau, Panama, Papua New Guinea, Paraguay, Poland, Portugal, Romania, Samoa, San Marino, Seychelles, Singapore, Slovakia, Slovenia, St. Vincent and the Grenadines, Sweden, Switzerland, Taiwan, Timor-Leste, Tonga, Trinidad and Tobago, Turks and Caicos Islands, Tuvalu, USA, Uruguay, Vanuatu and Vatican.
United Kingdom - Visa information website
UK Missions
Foreign embassies in the UK