I estimate that there are approximately 4,500,000 British passport holders living overseas. The following table provides a breakdown by country.
Passport issuing post Country Estimated number of British passport holders Buenos Aires Argentina 10,600 Canberra Australia 615,500 Vienna Austria 13,600 Baku Azerbaijan 2,900 Bahrain Bahrain 9,700 Dhaka Bangladesh 10,000 Bridgetown Barbados 33,700 Brussels Belgium 44,300 La Paz Bolivia 2,000 Gaborone Botswana 4,600 Rio de Janeiro Brazil 12,300 Bandar Seri Begawan Brunei 5,800 Ottawa Canada 232,600 Santiago Chile 5,600 Beijing China 15,000 Hong Kong China 798,800 Bogota Colombia 4,300 San Jose Costa Rica 7,300 Havana Cuba 700 Nicosia Cyprus 63,800 Prague Czech Republic 6,700 Santo Domingo Dominican Republic 1,600 Quito Ecuador 2,700 Cairo Egypt 14,000 Tallinn Estonia 800 Addis Ababa Ethiopia 1,500 Suva Fiji 1,200 Helsinki Finland 4,300 Paris France 206,200 Banjul Gambia 2,000 Dusseldorf Germany 181,500 Accra Ghana 6,500 Athens Greece 26,900 Georgetown Guyana 1,700 Budapest Hungary 4,600 Reykjavik Iceland 900 New Delhi/Mumbai India 37,700 Tehran Iran 3,000 Dublin Ireland 108,900 Tel Aviv Israel 57,800 Rome Italy 49,000 Jakarta Indonesia 12,000 Kingston Jamaica 23,700 Tokyo Japan 26,500 Amman Jordan 8,300 Nairobi Kenya 40,500 Kuwait Kuwait 7,900 Beirut Lebanon 6,200 Tripoli Libya 3,600 Lilongwe Malawai 9,200 Kuala Lumpur Malaysia 18,200 Valletta Malta 8,400 Port Louis Mauritius 8,300 Mexico City Mexico 12,600 Ulaanbaatar Mongolia 300 Rabat Morocco 2,800 Windhoek Namibia 1,400 Kathmandu Nepal 1,600 Amsterdam/Copenhagen Netherlands 78,500 Wellington New Zealand 215,900 Lagos Nigeria 16,000 Oslo Norway 19,200 Muscat Oman 7,600 Islamabad/Karachi Pakistan 35,000 Lima Peru 6,000 Manila Philippines 19,200 Warsaw Poland 5,700 Lisbon Portugal 22,900 Doha Qatar 8,700 Bucharest Romania 2,200 Moscow Russia 6,600 Riyadh/Jeddah Saudi Arabia 24,800 Belgrade Serbia and Montenegro 1,800 Victoria Seychelles 1,700 Freetown Sierra Leone 2,900 Singapore Singapore 51,500 Pretoria South Africa 174,600 Seoul South Korea 3,600 Madrid Spain 195,000 Colombo Sri Lanka 4,800 Stockholm Sweden 18,700 Geneva Switzerland 72,200 Damascus Syria 2,200 Dar Es Salaam Tanzania 6,600 Bangkok Thailand 45,600 Port of Spain Trinidad and Tobago 13,400 Tunis Tunisia 1,500 Ankara/Istanbul Turkey 12,600 Abu Dhabi/Dubai UAE 61,500 Kampala Uganda 3,700 Kiev Ukraine 1,100 Washington USA 527,500 Caracas Venezuela 7,200 Hanoi Vietnam 4,000 Sana'a Yemen 1,900 Lusaka Zambia 7,900 Harare Zimbabwe 25,100 Total 4,521,000