Postcard at bottom of page one is not dated but I would suspect inter-war.
Here is pic of that same period with the speedos of the time (but changing rooms had their own separate little buildings and the house came with the job for the Lido Manager).
It is as I remember it as a kid and is almost the same view as the modern pic just posted (and remains basically unaltered and it is still the only 12-sided in the country):
https://www.hillingdon.gov.uk/media/...38picture2.jpg