Catherine, I do not know of any Britnells from Wigan although the 1881 census gives a Cranley B Britnell, a railway porter, married to Matilda and living at 16 Byrom Street, Wigan. He was born in Chinnor, Oxfordshire (about 1830)and she in Bledlow, Buckinghamshire (about 1845).
They have children, Lancelot (1866) a colliery asst.Susanna (1869), Walter E. (1871), Matilda T (1872), John S (1874), and Alfred B (1877).
These are the only Britnell's in Lancs in 1881 although there are a couple of odds in Yorks.
Somewhere in New Zealand you should have my Uncle Frank if he is still alive, I don't know of any children. If he is still alive he will be about 78, he was my late father's younger brother, went out to NZ in the fifties I think.
I hope these are yours, no surprise to find them coming from the Bucks/Oxon border, all Britnell's seem to come from there within a group of about a half dozen small villages or hamlets: Bledlow/Bledlow Ridge/Radnage/ Chinnor/Crowell/Aston Rowant.
Good luck, let me know if you need help, my wife and I are busy researching our families at present so we may come across a link!