I don't think that the newsreel opening of Beresford Square is the same 'opening' in the photograph.
If so, why take photos of the event and sell as postcards, without including royalty in it ....

The crowd would also be much larger - the top level would be heaving with people - as it is three is only a lone woman overlooking proceedings.
Also, visible buildings around Beresford Square are a lot larger and grander whereas in the postcard the houses look like domestic dwellings and very small local style shops.