Thank you very much for the extra photos.
I confirm no. 4, see attached. The head has a distinct 'flat oval' form. There are other caterpillars similar, but none with this head form.
No.5:brains: It is a long time since I have hit an absolute brick wall in identifying a caterpillar, but I have definitely hit one now!
It is definitely an Ennomus type species, markings indicate Cepphis advenaria, but it is missing the essential white marking on the 4th segment across the dorsal to sub dorsal level.
I am still not discounting Cepphis advenaria, because the Ennomus type species can be extremely variable. There is enough evidence that all possible variations to the expected normals within this general group of 'Thorns' and 'Beautys' are not recorded. Humps are missing, markings are missing or different, colour is different. See the attached 'August Thorn' example which I have only been able to identified through rearing and hatching, this green variantion without humps is not found in publication yet. Barred Umber, and Peppered Moth are other cases I have recorded too.
I am actually not discounting the possibility no. 5 could be Barred Umber, but on a much lower probability. The only thing I can say is, if you ever find such an example again, take it home and rear it. Document the development stages in mm, that there is somewhere a record of another variable to a 'normal'.
I will now trawl through my past August and Sept photos to see if I ever had one like this, that I have perhaps forgotten about. Ah, I take it it is a recent photo, and not from May or June?
Best regards
Jim