RootsChat.Com

Possible sighting of John in 1881 in cavalry barracks in Leeds? (Birthplace "St Mary London" could possibly be Richmond - parish church is St Mary Magdalene). RG11/4524/136/14.

Consistent with the horsey theme at least

This might have possibilities - I will look into it.

The London Metrolpolitan Archives have the records I think, for wandsworth workhouse.
Do you have a copy of Richard Berens will??

Yes, I do have a copy of his will.

It's an odd phrase, but I wonder whether it meant she was in service as a governess?

What happened to Jane later on - presumably she gave birth to a child who was your great grandparent? Can she be found in a later English census to ascertain an approx birthdate, or is there some reason such as emigration which prevents this?

Richard Berens was a bachelor until he died, with no children.

Yes, it should be 19 Queen St. Mayfair.... 
In answer to your 1st question,  I haven't found her in the 1851 or 1861 census as I don't know which Jane she would be... I wondered, if given the fact she worked for a prominent citizen, after Berens' death in 1849 would she have been able to use her reference to work for someone else of the same calibre? 
I know my great grandfather John Murray was born in 1862 in either Richmond or Chertsey, Surrey (depending on the census).  No birth certificate has been found - he claimed his mother died when he was 12 leaving him an orphan and a 'stable boy' - he never mentioned siblings... to be raised by an 'Aunt Ellen' ?...  He never talked about his mother or lack of father.
There is a  Richmond, Surrey parish record I have showing a 'single woman Jane Murray' having a son John Murray born in 1860 but christened 1862 - her last residence 'Aldham Park, Herts'... but the 1861 Aldham Park census doesn't show a Jane Murray, and I don't know if this is them.
 John Murray married Emma Cole in Battersea, Wandsworth 1883.  He finally shows up in a census in 1891 - a Coachman at 16 Compton (?) Mews, Kensington.  He states on his marriage certificate that his father is "John Murray - Butler", but I think he made that up.  He never spoke of a 'father' to his kids except to say once that his father was a 'Scottish Chieftan'!. 
A few days ago I found a burial record for the Wandsworth Union Workhouse showing  "Jane Murray 36 years" dying in 1872 (which would have made John around 12 & would fit with his story), but to think a woman that worked near Buckingham Palace for the uppercrust, would possibly end up in the workhouse is hard to believe...  the other interesting point I have is John was very cultured, played the organ, painted, could read/write, fabulous carpenter and carver, poet and became a well dressed Coachman... we just don't know where or how he learned all this on his own.  It all adds to the mystery and I'm determined to solve it...

Thanks so much for checking!  You've saved  me a lot of unnecessary searching.
Carol