Thanks for your help and advice. Your findings on the Census returns match mine starting with 1841 in St Luke, Chelsea. He disappears in 1851 and re-appears in 1861 as a married man with Hannah in Whitecross Street, near Shoreditch.
Both couples seem to have come from wealthy families. John's father was a starch manufacturer (later made bankrupt) and Hannah Coward nee Taylor' s father was an engraver. The 'Hannah' that was in the 'Workshouse' in Edmonton in 1851 has an age that doesn't fit but her birthplace does. John Coward totally disappears in 1851. It really is a headache!! But I'm not giving up.
As a Master Shoe Maker perhaps there are records that might pin him down (I hope!!!)
Many thanks for your help.