Also got sight of a new photo. I think beta is in the middle with Massey Shaw to the left. Not sure which the other is but would guess Gamma. Will have to recreate this when back in London.
A prize for anyone who can identify the building in the background. My guess would be the MI5 building but not sure…
UPDATE: Just found this photo on a norwegian stock photo site. It has the following caption:
“As part of the formal opening of the London Fire Brigade headquarters building on the Albert Embankment, London’s fireboats Massey Shaw, Beta III and Gamma III lay off the headquarters foreshore together with the Brigade’s fireboat tenders. Date: 1937”
betaiiifireboat 
Gamma II on the left,Massey Shaw in the middle and Beta III on the right. How can I tell? by the number and set out of the round port lights.
Gamma II 6 forward one offset.
Massey Shaw 4 .
Beta III 6 evenly spaced.
The building is Thames house, Milbank aka MI5. The photo is taken from the fireboat pier outside Lambeth fire station ,Albert Embankment
Eagle eyes there. You are definitely right on the spacing of the square windows.