When you are travelling to United Kingdom with a U.S. Passport, a Tourist Visa is not required for a period of 6 months.
In case you hold a passport from another nation, you need to produce the following documents:
Original passport and old passports, if any
Your passport should be valid for at least 6 months from the date of submission of the visa, with a minimum of three blank pages
Confirmed return air tickets
The visa application form duly filled (online) by the applicant.
2 recent passport-size colour photographs taken against a white background with matte-finish (size 35 mm x 45 mm and 60% - 80% face close-up) (Photo specifications)
Note: Photograph should not be more than 3 months old, scanned/stapled and should not be used in any of the previous visas.
Covering letter mentioning details of travel, details of the traveller, purpose of visit and duration of stay. The letter should be duly signed by authorized signatory with company stamp and addressed to the Visa Officer, British Deputy High Commission, Kolkata.
Income Tax Returns of the last 3 years
Original bank statements reflecting transactions for the last 6 months, duly attested and signed by a bank official
Proof of investments
Hotel confirmation details