Originally Posted by jackiedada

You require a Direct Airside Transit Visa (DATV) as per government regulations. They may not be check 364 days of the year, but the day they decide to check it may be your unlucky day. Here is some more information from the UK Border Agency website.
http://www.ukba.homeoffice.gov.uk/vi...ansit-airside/

From first hand experience, I do know several of my colleagues who have used BA for BOM-JFK and have transited LHR without a DATV.