Do ALL nuts/sharp edges need to be covered - ie the ones inside the envelope of the wheel? Such as the brake calliper screws, bleed nipple etc?

All stuff that it'd be pretty much impossible to come into contact with......and if you did it'd be the least of your worries!

They only test what can be contacted from the front of the car not the back, i wish i knew this before i started sticking on my rubber trim as i could have cut my time down by half

I'm pretty certain that anything that falls inside the alloy wheel does not get tested.

HTH
Dan

Anything forward facing which can be contacted with a 100mm sphere

I put nut covers on every bolt-head, nut, bleed nipple, damper adjuster in sight. Better ten too many, than one too few.
They might start to fall off now as I finally passed SVA today