Dont know Catherines surname yet.It was very rare for regular people to marry others,even 4 streets away,let alone between Cowley and London.
Once we have Johns military records,then we should get some clues.Unfortunately,the records for the Guards regiment were mostly destroyed by bombing at the Guards Chapel in Birdcage Walk.Maybe this is where John was the Chapel Keeper?.
So he could have met Catherine,whilst recruiting in Oxfordshire,or as there is no record of a marriage,there is always a possibility that he married her on service.
Regiments were allowed to take 6 wives per company on active service,where they shared the hardships with the men.If their husbands were killed,they were generally remarried within 2 to 3 days(its a possibility for our John and Catherine)
Given Johns age in 1815,its possible that he served in the guards from 1795 and could have been present in the American wars and the Peninsular wars against France.this is where he could have married Catherine...Maybe the Catherie you found married to another man is the correct Cathy after all.I wonder if he was in the same regiment as John and died in battle,and then our gallant GGFx5 married her??
Essex Lad!!.Unfortunately no...Essex old lad yes..
If you look on Facebook under Lawrence Phillips you should see a photo of me driving my famous rich lady guvner to Liz hurleys wedding in the days when I was a house butler/chauffeur.