It depends a bit on the site rules.
Legally it is a defence (which I have used) to show to the HSE that any alternative you have put in place must provide protection at least as good as that required by the regulations, i.e. did the netting provide the same protection as tethering?
On the average construction site I would doubt it. Even a one inch hole, large enough for a small screwdriver (and I'll bet I could find one!) in the whole of the netting would put you in breach.