Notes from AMO's Historic Buildings Appraisal for Nos. 2, 4, 6, 8, 10 and 12 Observatory Road:
The buildings at Nos. 2, 4, 6, 8, 10 and 12 Observatory Road were built in 1955 to replace a row of colonial villas (known as “Observatory Villas” [Tin Man Toi Ok U.] 天文台屋宇) built around 1902. The ownership record of the site can be dated to around 1875 when lot K.I.L. 615 was sold to one of the famous Parsee merchant Framjee Hormusjee, who had operated in the opium trade in Canton (now Guangzhou) during the Qing Dynasty.
Subsequently, a row of villas, i.e. “Observatory Villas”, were built and sold house by house. One of these houses was subsequently sold to Samuel Macomber Churn, the chairman of Hong Kong Motorcycle Association.
Demolition date is a guess, based on the next set of buildings being built in 1955.
Observatory Villas 
About the 1930s photos of Waterloo Road in the string headed "A Kowloon Street," David remarks that the soldiers may have been surprised to find a piece of suburban England in Kowloon. This is echoed by the HK Telegraph's description of the newly built Observatory Villas in Kowloon in 1905. If the Ladies Directory is correct, my Warren grandparents, Charles and Hannah moved out of the parental home into one of the newly builit houses. Here is the article as recorded by Carl Smith:
1905, Jan. 6 – HK Telegraph – Kowloon Developments – Great improvements during 10 years. Might be a suburb of London as far as outward appearance – though a visit to the rear where Chinese servants are everywhere in evidence dispels illusion. One of the latest sites to be covered with housing is that belonging to Mr A.V. Apcar, on Observatory Road – will include 22 houses – six are near completion, expect to be ready in early April, 5 rooms – two public (joined by folding doors) 3 bedrooms – bathrooms available – two storeys, with high basement below. European kitchen. In front of each a garden, and to rear a tennis court. Estimated cost $11,000, designed by Mr John Lemm, F.I.A., NSW, M. San Institute. Will be known as Observatory Villas. Hong Kong is fortunate in having a suburb so admirably situated.
Re: Obervatory Villas
I think in this aerial shot: http://gwulo.com/node/6649
should be visible.
Re: Obervatory Villas
Thanks for the extra information - not many gardens and private tennis courts in TST now!
I've added the photo,
No. 2 K.I.L. 615 R.P. …
Observatory Road (north side) - Villa No. 6 is towards Chatham Road and Villa No. 1 is towards Kimberley Road
Observatory Villas ("Tin Man Toi Uk U")
No. 2 K.I.L. 615 R.P. "Observatory Villas" No. 6
No. 4 K.I.L. 615 R.P. "Observatory Villas" No. 5
No. 6 K.I.L. 615 R.P. "Observatory Villas" No. 4
No. 8 K.I.L. 615 R.P. "Observatory Villas" No. 3
No. 10 K.I.L. 615 R.P. "Observatory Villas" No. 2
No. 12 K.I.L. 615 R.P. "Observatory Villas" No. 1
Source: 1938 Street Index page 262 (image 478)