I don't know about corrigiendum letters as such. I've got the downloadable CAP 493 with Amendment 57. It mentions no VFR clearances when the vis is below 5000 m but I can't see anything about cloud ceiling.
I'm not just trying to be nitpicky about details, though you know too well that's in my nature
. Under ICAO rules for controlled airspace, the minimum VFR level permitted is 500 ft and the minimum vertical separation from cloud is 1000 ft. Thus VFR is impossible if the ceiling is less than 1500 ft. The UK has neither rule and so VFR is, in principle, possible with such a ceiling.
The ICAO rule anticipates class E control zones where a clearance wouldn't otherwise be required. It forces a flight in such circumstances to get a SVFR clearance. In the UK, the same can be achieved by instructions to ATC, as all the flights in the CTR require a clearance.