At county fairs around here, the local power companies put on electrical safety demonstrations. One of the things they show is what happens when you touch a high-voltage line with a seemingly non-conductive piece of dry lumber. One word best sums it up: Zzzzzap! It's my understanding that practically anything hanging from high-voltage main power lines is potentially conductive, even a crepe paper streamer.

One thing I've noticed about crepe paper streamers is that they tend to wad up into a ball as they fall, and are not likely to end up draped over power lines. Even if they are, the first hard rain (a daily event in the UK) will cause them to break and fall.