I may have been thrown off by how "late fall" all the other vegetation looks in that first photo. And those purple pot plants just always look done to me.
As I understand flushing, it is most employed by hydroponic growers who are providing all of the nutrients all of the time. Ramping up nutrient concentrations to maximize growth needs to be compensated for by reducing concentrations in the end so as not to compromise flavor.
In soil, the logic is much the same, but the mechanics of flushing does not work as well and presumably there are not as many residual free nutrients within the root zone.
So I would think that so long as you have not been adding large quantities of nutrients in your waterings, flushing may not be an issue.
As for harvest ready: what few pistils I can see look brown and withered. I'm sure you know the old clear/cloudy/amber trich assay.
I am reminded you are in the UK and were concerned about mold. Looks like you might have survived the weather.
I suspect the fall chill will put an end to further development, and thus the idea of securing the harvest seems appropriate.
I am very interested to see how those flowers trim up.
