TC - so you're saying that National Grid are going to effectively cease operations of their 3xAS355? I'm not aware of them doing anything else with those aircraft than powerline surveying.
There are not many others that do powerline surveys - WPD Helicopter Unit is the obvious one that springs to mind. Pipeline surveys, well, you can add a few more that do that work - who flies the Esso route these days since Southern Air went under?