If you think that one or more of your ancestors might have registered a birth, marriage of death overseas then you might want to consider searching on the website http://www.bmdregisters.co.uk/ This company offers access to registers that are housed in The National Archives, Kew and are under the accession numbers RG33, RG34 & RG36. I have copied the description of the contents of these registers below from the website.
RG33 – Registers of Overseas Birth, Marriage, death and Burial of British Subjects including those onboard ships. Also Lundy Island Devon. Original registers, notebooks and copies of entries in registers kept by incumbents of English churches and missions, British embassies and legations etc. These cover the period 1627 to 1960 and are very detailed.
RG34 – This series contains marriage certificates issued by foreign registration authorities and churches, copies of entries in the registers kept by British embassies, incumbents of English churches and chaplains, notification of marriages of servicemen during service abroad, and documents deposited for safekeeping. 1861-1921
RG36 – This series contains Registers and Returns of Births, Marriages and Deaths in the Protectorates etc of Africa and Asia Covering dates 1895-1965. Notifications of birth, marriage and death forwarded by officials responsible for civil registration under administrative ordinances in Nyasaland, Kenya, Somaliland, Uganda, Sudan, Palestine, Sarawak, Malaya, including Johore and Selangor, and British North Borneo. These newly added records were previously only viewable on microfilm at The National Archives.
Standard searches are free, but to view scans of the actual documents you need to either buy credits or purchase a subscription. Credits cost 50 pence each and each scanned image will cost 5 credits, an advanced search will cost one credit and may help when you have multiple choices of names to choose from. A one year subscription costs £68.95 and this includes access to many more records on the sister site www.thegenealogist.co.uk