Tony, your post of the ad in Picture Post reminds me of many similar pieces of photo history that I've seen on my visits to Ilford in Mobberly. They have adverts for their first version of VC paper dating back to about 1948/5 including some early work on split grade printing by the late Jack Coote including a cardboard hand made T shaped filter with a 0 filter on one side and a 5 filter on the other. I've had some great times in the R&D department in Mobberly looking at the history of the company and on the same visit working with them on the development of Warmtone and Delta 3200.
I'm very sad about the current situation and have lost touch with many friends in Ilford as a result of the recent redundancies. I hope and pray that things will get no worse.