Details: I hold a Indian passport with a valid and unexpired US student visa (F1). I would be travelling from Los Angeles to Mumbai via a 18 hr layover at London Heathrow airport in December 2012.
1) You don't have to apply for a transit visa if you are eligible for a Transit Without Visa (TWOV) concession. The rules for TWOV are outlined here: http://www.ukba.homeoffice.gov.uk/sitecontent/documents/policyandlaw/carriers/ukvisarequirements.pdf
Indian citizens may not TWOV in general. However, it looks like you meet the following exception:
So you should be able to TWOV.
2) You can do sightseeing.
protected by Ankur Banerjee♦ Jan 20 '13 at 1:24
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