A 2 A.  Enables you to locate the UK record offices & to search records. (Free site)

Ancestry.co.uk  

Enables you to search a very wide range of records see below     (not cheap but comprehensive)

UK Census records:  England/Scotland/Wales 1841-1901

English Settlers in Barbados
Slave Registers of former British Dependencies
British Phone Books
British Army WWI Pensions
England & Wales BMD Indexes
UK & Ireland Parish and Probate Records
WWII Newsreels
Photos
Stories
Pallot’s Marriage Index

NOTE Ancestry.com the American site will automatically send you to the UK site.

Australia (NSW). Births until 1905 & Marriages and Deaths until 1945.