In the 1881 census William H Gill (a British subject born in Sicily) and his wife Harriet, five daughters, two sons, mother-in-law, sister-in-law, nurse and cook are living in Hatherley Road at unnamed and unnumbered premises next to a building called Wavertree.

Wavertree appears to have been 29 Hatherley Road so possibly William Gill was at 31

Going away from Sidcup High Street buildings remain intact as far as Granville Road (No 19), beyond that Hatherley Road has been completely reconstructed as far as 87 and that must include Gill's abode.

In that census Gill is listed as "Clerk Genl PO London (CSC) & Organist"

By the 1891 census there is another house "Kilkenny(?)" between the Gills and Wavertree. There is no mention of "Mona" on either census.

In 1891 he is living with his wife, four daughters, one son and a niece and nephew and is shown as "Civil Servant Clerk GPO"

I think this photo is indicative of the sort of building it would have been Hatherley Road 1900 not as you might imagine a cottage.