Well the board used for mounting isn’t contemporary with the flag in the photograph. Hurlock Brothers were using that “Royal Crest” trademark from 1901 onwards; but, since it says “registered” underneath, then the board must have been produced after the registration date, which was 18th September 1917 (and continuously renewed until 1977, expiring 20 years later).
That metal tripod appears to have a large block of masonry hanging from a winch with chains. Surely that's going to be a foundation stone for whatever is being constructed. If you look for period pictures of new buildings being dedicated, that winch arrangement is commonly seen with the foundation stone being lowered from it.