Can anyone find their marriage please?

[Joan of Archives]

So I have looked for this marriage for ages & no joy.

Margaret CAMPBELL born Edinburgh approx. 1848/49, marries either George William COOPER b 1843 Arlesey Beds or William George COOPER b 1845 Arlesey Beds around 1866-68 if we are to believe what she put on the 1911 census

George W & William G were brothers & the sons of George & Hannah COOPER living in Arlesey Bedfordshire where the Coopers have lived since the early 1450's (that bit was bizarrely easy!) Obviously they didn't have much imagination naming their sons! Unfortunately they seem to sometimes drop one of their first names on subsequent censuses!

Their first child I can find registered to Margaret CAMPBELL COOPER was in 1866 March Q Hannah Cooper, mmn CAMPBELL in Wandsworth.

I've tried every combination I can think of for this CAMPBELL/COOPER marriage but never found it, so either they had 15 kids without bothering or they could have married in Scotland or abroad?

Any ideas welcome!

Thanks