Hello again and thank you for all your replies. it would seem likely that his spelling is an attempt to phonetically spell Stonebrook in German (Stohnbrock), and that his real surname is still not clear, but probably one of those suggested.
Garstonite - yes this is his marriage at aged 42 and he says he is a widow when he marries Mary Attwood on 10 October 1834.
One thing this has just brought to light though, is that there is another marriage listed in quarter 4 of 1849 for Johan Stohnbrock (Bethnal Green); on the same page is also Mary Attwood, so I'm not sure what's going on here?
I need to post a request to see if someone has the actual image of this marriage
Mar