I'm not sure about the CHC & Bristows numbers. They seem a little low.
Bond will also probably be a little higher. I think that they've got 6-7 332L2s at Aberdeen and 20-30 EC135s & Bo105s.
PremiAir is closer to 30. 15ish AOC aircraft, a handful of managed aircraft and the Police EC135s. Maybe that would put PremiAir into 4th place.
But thinking about it, Cabair and HeliAir probably also operate quite a few Robinsons each for training. I'm not sure what the numbers might be though. Did you want to include training providers?