The General Register Office has not been at Somerset House since the early 1980s, it moved to St Catherines House, that moved in the mid 1990s to the Family Record Centre but next year that is closing and the GRO is moving to the National Archives at Kew, and access online is being increased in time for that move. What we can get online now is fantastic, but when it moves, it will vastly improve and increase.
Google freebmd. The transcription, (done to a very high standard), is not complete but charts are displayed to show progress.
Don't believe that you will find the answers to all events as it has been estimated after a searching study, that there are an estimated 1M errors and omissions between 1837 and 1900.
I use Ancestry for recent events (last 50 yrs or so) and freebmd for earlier. You can order bmd certificates online here http://www.gro.gov.uk/gro/content/ if you have the index number each cert cost �7