[Nuvistor]

Half Wave rectifiers did cause a problem for the CEGB but it was relatively short lived in the scheme of things, bridge rectifiers were introduced into the power supplies, it put the chassis at half mains voltage but that was another problem.
I have heard of the audio groups discussing DC on the mains and suitable equipment to buy to cure it. If you can’t hear much from the transformer I wouldn’t worry about it, more likely poor installation or loose windings will cause more of problem.

Edit, just noticed Sidebands post.
The CEGB complained about it in the middle 60’s from what I recall, made worse when the heater circuits included a diode, that meant only the +ve half cycle was in use. The change over to the power supplies with bridge rectifiers brought their own problems as you state.
I always thought it was just me who didn’t like the half mains chassis idea, seems I was not alone.