Hello bunty
Thanks for your input. Since my initial post, here's what I've found. On my O'Brien side, my ggrandfather, William Brien was born in Shanacashil, Cork in Apr of 1840. His parents are listed as William Brien Sr. and Norry Horgan. Sponsors at his Baptism were Daniel Brien and Joan Manley.
William Jr married Johanna Connelly on 26 May 1872 in Drimoleague Parish. Witnesses were Denis Connelly and John Murray. Johanna Connelly was born Aug 1851 in Cooragannive, Cork. Baptised in Caheragh Parish 31 Aug 1851. Sponsors were Pat Connolly and Anne Browne. Johanna's parents were Cornelius Connelly and Johanna O'Brien. Another name that keeps appearing on this side is Crowley,
On my Collins side, my grandfather was John Collins, born 3 Jan 1876, Killinga, Cork. His parents were Thomas Collins (b. 1841) and Mary McCarthy (b 1842). Sponsors at his Baptism in Kilmacabea Parish were Joseph Brien and Margaret McCarthy. Thomas Collins' parents were John Collins and Mary Flynn. Mary McCarthys' parents were Dennis McCarthy and Hanora Hurley.
I've not found any relatives on either side who migrated to England, but your history is a little earlier, so I wouldn't rule out a possible connection in previous generations. I've had my dna done and am connected to Ancestry.com and GEDmatch.com
Phil