That's too expensive for the likes of the UK police units to commit to, I suspect. We already have TCAS, but I notice, no-one in the Air ambulance world carries one, again due to the fact that they are charitable and cannot afford such niceties.
I believe there is an alternative in that the moving map systems we fly with offer an option to 'warn' when flying near marked wires on their maps. Don't know anyone who has one ...yet.
The take up on these is slow I suspect because of the good stats for emergency services helos. Touch wood, all those flying 'normally' and within laid down guidelines, have not had occasion to conflict with wires. [I chose my words carefully].
That's not to say we could never hit wires, it is just a rare phenomenon... long may it last, please