Jobod on Family Tree Circles

LOOKING FOR WILLIAM JONES born 1848 in Finsbury, Islington, London.

I know he was married in 1875 to Mary Cankett in Newport, Monmouthshire, Wales (I have certificate), and at that time his father DAVID was deceased. My problem is that I have yet to locate WILLIAM's birth certificate details. Many pounds(?) have been spent obtaining incorrect certificates!
I have to admit that I am not 100% sure that WILLIAM was born in London, but details from Ancestry.com suggest that he was so born!
There has been 'no joy' with census returns for 1841, 1851 and 1861, where I was hoping to locate the whole family before DAVID died.

Any help would be very much appreciated.

Have been researching my own family of BURDETT for
some 40 years, I can show a direct male line from my
Grandsons to Erasmus in 1575.
Now come across a 'stumbling' block and
need to hear of the names, dates and places of wife,
father and mother of:
Erasmus BURDETT, born about 1575 in Countesthorpe,
Leicestershire, and his wife, father & mother.

It is my hope to be able to trace a direct lineage back
to the 'Conquerer'. I've already traced forward from
986 to 1352, but things like the Black Death etc. have
hampered my investigations.

Any help in either of these directions will be of utmost
use to me, and very much appreciated.