I feel your pain. I started down this road about 11 years ago and have so far gotten 2 generations down. My ancestor was, according to the 1851 census, born in 1803 in Westminster (City of Westminster in greater London). I made a list of all parishes in Westminster and searched their baptismal records on Ancestry or on Microfilm from LDS. I found 2 births listed with his name in 1803 and tried then to follow all the births to the same parents in that parish for 10 years before and after 1803. Bingo-one of the families had children with exactly the same names as my ancestor's children. Then you rinse and repeat. A mixture of luck and lots of patience.