The Burial Index on find my past contains an amalgamation of mnay other indexes and sources that have been collated and then re-indexed for thier subscribers.
Amongst their index will be the records from the National Burial Index project completed by the Federation of Family History Society members:
http://ffhs.org.uk/projects/nbi/nbi-overview.p hp
in which you will find a variety of information. The International Genealogical Index has also been used, though you can also search this on the LDS website at
familysearch.org.
Various Parish Registers of Burials have been used as well as other regional and national collections like the City of London Burial Index.
When you are searching for a burial you need to think of two aspects, one is the actual funeral which if held in a Church or chapel meant an entry in a Parish Register for Burials, if it was a civil burial you need to look at civic cemetary records and some of these have been included in the National Burial Register.
The other aspect which is far nore interesting and revealing are the Monumental Inscriptions, which have been part of why the Federation of Family History Society have been able to maintain their charity status. Many regional Family History societies and local history societies have carried out the recording of inscriptions on gravestones in an accurate and organised uniform way over the last 30-40 years and these are available thru the FFHS and member societies at a nominal fee.
Burials in parish registers would include the name, age and later on the occupation and residence of the deceased.
Some Parish Churhces would also have a grave register which would have a plan of the graveyard and numbers of graves and the grave occupants and owners. I don't think these are on the FMP burial index.