Checked a few years back and the group discount would appear to be a thing of the past. Despite checking it out with credit unions where they are currently advertising discounts this does not appear to be the case any longer.
My health insurance was under a group scheme.
The group discount aspect of it seemed to disappear on a unilateral basis i.e. we are discontinuing it and you can do what you like.
Also, there was an extra charge if you sought to pay your premium monthly by direct debit.
It was cheaper to pay the annual premium in one go if your finances could bear it in January.
I even asked if there was a discount for paying the annual premium in one go - not a hope