I too would like to know the answer, as the opinions have differed when I've asked previously about surplus .303.
Here's what I've gleaned, and perhaps others with more knowledge can correct/add.
The "z" in the VIIz indicates nitro-cellulose, rather than Cordite, so that's a plus. The primer may, or may, not be corrosive. I've found no single source of clarity on this, but the DI stuff should be, looks to be, Boxer primed, so is reloadable.
For my part, I intend to treat all ammo of this vintage as corrosive, and clean my rifles accordingly, and will take a peek to count the primer holes every time I access a new box.
Don't think I shed much more light on this, but it's all I've got.