This description is provided by Olive Thexton of Fylde Branch

BMD is the abbreviation often used by family historians for  the national index of  Births, Marriages, Deaths.

For England and Wales, registration of a birth depended on someone who knew about the birth -- usually one of the parents -- actually going to the Local Office to register it. 

Civil registration for England and Wales began on 1st July 1837 and continues to the present day.

The index to the records is held in London, previously at St. Catherine's House, but now at the Family Records Centre, 1 Myddelton Street, Islington, London EC1R 1UW

The main indexes are in book form, and arranged quarterly, then alphabetically by name within the quarter, but many people now consult them on microfiche at a reference library, or at a county archive or record office. Remember that to see the fiche, you will usually need to book a reader machine, so planning ahead is advisable. 

The index is used to locate information on birth, marriage, or death, and each entry has a reference number that may be used to order more detailed registration certificates directly from the UK's Office for National Statistics. 

Records for Scotland commenced 1st January 1855.

Records for all Ireland run from 1st January 1864 to 31st December 1921. 

After this, births, marriages and deaths in Northern Ireland from 1 January 1922 are at  held at Customs House, Belfast. (except those marriages conducted by Roman Catholic Clergy from 1 April 1845 to 31 December 1863).