Here is a link to Keith M Jordan's "The Inner Ring Road Underpasses & Murals of Birmingham" page 3 (9/67) includes a photo of the Hill Street subway:
Hi Stokkie, thank you very much for your reply, I clicked the link but it comes up with a blank search result as though the search has timed out. I will try again. I am after a view inside the subway around that time frame within the 90s would be ideal but it seems very rare if not impossible to find any. Thanks again!Birmingham Archives have photographs from 1961. These are not digitised though. I don't know if this is any use to you.
https://calmview.birmingham.gov.uk/CalmView/Overview.aspx
Stokkie
smashing photos thanks for sharing themHere are a few photos pre and post 1960's development