hey aka169, below is what I found from their website. My bro came 2 mths ago from Nepal via UK in F1 visa, he said no one asked him a thing. I don't know why a US Permanent Resident would need a visa to fly via UK, but please do let us know after you call them. Thank you. Source: http://www.britainusa.com/visas/articles_show_nt1.asp?i=65025&L1=41000&a=41448 Direct Airside Transit Visa Passport holders from the following countries require a Direct Airside Transit Visa to transit the United Kingdom. This is the case even if you only intend to: Remain airside Stay on the plane Not pass through UK Immigration You will need a Visitor in Transit visa if you need to pass through UK immigration to: Change airports Change airlines Stay overnight (MAXIMUM STAY UP TO 48 HOURS) COUNTRY NATIONALS REQUIRING DIRECT AIRSIDE TRANSIT VISA: AFGHANISTAN, ALBANIA, ALGERIA, ANGOLA, BANGLADESH, BELARUS, BURMA (MYANMAR), BURUNDI, CAMEROON, PEOPLES REPUBLIC OF CHINA, COLOMBIA, CONGO-BRAZZAVILLE, DEMOCRATIC REPUBLIC OF CONGO (ZAIRE), ECUADOR, ERITREA, ETHIOPIA, GAMBIA, GHANA, GUINEA, GUINEA-BISSAU, INDIA, IRAN, IRAQ, IVORY COAST, KENYA, LEBANON, LIBERIA, MACEDONIA, MALAWI*, MOLDOVA, MONGOLIA, NEPAL, NIGERIA, PAKISTAN, PALESTINIAN AUTHORITY, RWANDA, SENEGAL, SERBIA AND MONTENEGRO, SIERRA LEONE, SOMALIA, SRI LANKA, SUDAN, TANZANIA, TURKEY, TRNC, UGANDA, VIETNAM, YUGOSLAVIA, ZAIRE (FORMERLY DEMOCRATIC REPUBLIC OF CONGO), ZIMBABWE. If you hold a passport from one of the above listed countries, you will need a visa unless you qualify under one of the exemptions listed below. EXEMPTIONS: Certain exemptions to this requirement have been introduced and apply to all DATV nationals. The following categories of traveller are not required to hold a DATV and may still benefit from the Transit Without Visa (TWOV) concession. YOU ARE EXEMPT IF: You are travelling FROM the US with a valid US visa and a valid airline ticket for travel via the United Kingdom to another country; or You are travelling TO the US from another country and hold a valid airline ticket for travel via the United Kingdom and a valid US visa; or You last entered the US with a valid US visa which has now expired but you hold a valid airline ticket for travel via the United Kingdom to another country and you are intending to transit the United Kingdom within 6 months of your last date of entry to the US; or You have a valid US I - 551 Permanent Residence Card (Green Card) issued on or after 21 April 1998 (but see Note 1 and 2 below); or You have a valid US Immigrant Visa packet (form 155A / 155B); or You have an expired I - 551 Permanent Residence Card (issued on or after 21 April 1998) and a valid I-797 letter issued by the Bureau of Citizenship authorising its extension (but see Note 1 and 2 below); or You have a valid Canadian Permanent Residence Card issued on or after 28 June 2002; or You have a valid common format Category D visa issued by EU/EEA member states; or You have a valid common format EU residence permit issued under Council Regulation (EC) No 1030/2002; You hold a diplomatic or a service passport issued by the People's Republic of China; or You hold a diplomatic or an official passport issued by the government of India; or You hold a diplomatic or an official passport issued by the government of Vietnam.