Hi Nicola,
Just going through unanswered posts and I came across yours.
If you haven't already got this information by now, then the missing 1871 census for William Northam is below:
RG10/2040/74 page 1
Glebe Farm, Upottery, Devon
William ANSTICE, Head, married, age 60, farmer of 90 acres, born Upottery, Devon
other ANSTICE family then
William NORTHAM, servant, single, age 12, farm servant, indoor, born Yarcombe, Devon
Best wishes, haliared