This may be helpful
( from
https://www.gov.uk/research-family-history )
Find index reference numbers online
You can:
search the GRO online Index of historic births (1837 to 1916) and deaths (1837 to 1957)
view index reference numbers for free on the FreeBMD website
Commercial companies also have the index reference numbers online, but you’ll have to pay to search them and prices will vary.
Find index reference numbers in person
You can also search for free at:
the Library of Birmingham
Bridgend Local and Family History Centre
the City of Westminster Archives Centre
Manchester Central Library
Newcastle City Library
Plymouth Central Library
The British Library (you’ll need to register first)
These are the only complete copies of the full sets of index reference numbers. They’re on microfiche.
Some of the index reference numbers are available at local libraries, archives and other locations.