Hi,
Having some local knowledge, I am suspecting either a TT earth rod and a big fault not being properly cleared causing a voltage differential or a fault with the cable supplying the tower, this also causing a voltage differential. The owner of the dogs was quite close to the tower when the dogs had the episode.
There was some supply from the tower the night before to supply additional lights, I wonder if there has been mistakes with this supply. There is a dusk - dawn lanten on the top of this tower, if the neutral had been disconnected and also a N-E fault then it is possiable that the TT rod could have become live and then have step potentials round it...