Thanks to you all for the rapid response. My ancestor is a Joseph Jonathan born about 1786 in the village of Llansawel in Carmarthenshire, at least that's what he reckoned in the 1841 census. The surname Jonathan whilst not common is nevertheless one which crops up a lot in south west Wales so maybe an extended family. I cannot find a record of him marrying Anne but some of their children were baptised although not all it would seem. Looking at census records there's a Timothy Jonathan in the same village born the same time so maybe twin brothers. I just don't know.