Many thanks for your replies. I've been doing some more research on Patrick and Catherine's time in England and it looks like I had my dates wrong originally. Patrick was born around 1843 so he emigrated to England later than I thought, probably sometime in the 1860s. Looks like he was alone when he did so.
Catherine also emigrated from Ireland (although I don't know which county) with her parents Bridget and Michael, possibly during the famine, and met Patrick in Boston.
Patrick died in 1897 in Hull, which is half an hour down the road from me, so I'll be going to try and find his grave before my parents and I visit Ireland in a couple of weeks. I'm not sure about his religion, and as yet I don't know anything about his parents.
Catherine's parents were born in 1818 (Michael) and 1826 (Bridget) but a name like Clarke is probably going to be far more difficult to research.