§ Mrs. Dunwoody
To ask the Secretary of State for Foreign and Commonwealth Affairs what the visitor visa requirements are for US visitors to the UK. 
§ Mr. Mullin
Nationals of the United States of America do not require a visa to visit the United Kingdom for less than six months. However, on arrival in the UK, they must be able to satisfy an Immigration Officer that they qualify for entry as a visitor under the UK Immigration Rules. From 13 November 2003 an additional entry clearance requirement was introduced for nationals of 10 countries, including the United States, who intend to stay in the UK for more than six months or who are work permit holders. Further information is available at UK visas website, www.ukvisas.gov.uk.