I don't know which place I mean, just on the list of births there is a place called Newington, volume reference each time it is mentioned seems to be 1d followed by the page number. Marylebone is 1a, Holborn and Islington Bc, Whitechapel and Bethnal Green 1c, etc. I thought perhaps as it seems to be surrounded by the other old Middlesex places it might be in Middlesex too.
Liz
ps. If it is in Middlesex, it just means I have another list of possible birth records for g.grandad!