Hi all, thanks for the suggestions.
Catriona, I hadn't thought of poorhouse records - one to follow up.
Frances, she's the one marrying James Miller & although the IGI says its a submission they are actually in the OPR for Ayr and, another one to follow up, recorded as being married by Rev'd Mr Schaw. I'll need to check if he was an Established Church minister or another & if so which.
I must say that the names of their children bother me slightly if her parents names were as given. There is neither a Dennis (perhaps not too surprising) nor a Margaret. The daughter in Ayr is my gggrandmother Cecilia & we know that she got her name from her paternal ggrandmother who was still alive, aged 86, at the time of her birth. However, the other children were in order James, Jane, Elizabeth, Alexander, John & Agnes. James & Jane were James' parents, Elizabeth was his sister (possibly twin), John was his grandfather & Agnes was presumbably called after her mother. On the other hand perhaps they didn't believe in the Scottish naming convention - it just seems strange when the other bits of my family stick to it so closely! Cecilia did have a daughter called Margaret as did her brother James but neither of them had a son called Dennis.
That leaves Alexander. I did wonder if Dennis was some peculiar short form of Alexander (a misheard Derry perhaps) but that didn't show up on any records. I also checked for the birth of an Agnes Harper & in the 1841 census for a Dennis Prentice & for a Margaret Prentice without success. The names, particularly Dennis, seem to be quite unusual for someone to get wrong. I've discovered Margaret recorded as Martha & an Isabella recorded as Elizabeth in similar circumstances. The Prentice is quite clear on the marriage record (altho' spelled as Prentise) so she must have been known by that name.
At the moment I could cheerful strangle her & her parents

I'll keep you posted if a big light goes on somewhere!
Muriel
Searching Ross - Lochwinnoch & Eaglesham, Renfrewshire; Glasgow; Glover - Paisley; Macadam - Glasgow.