fuel constraints - maximum of 60-70 mins airborne. 5 min transit each way leaves approx 50 mins on task. They need to comlpete approx 4 or 5 runs to DCO, and therefore the range from Leuchars is often critical.
Not so long ago, they generally operated between the Y70 and the coast, which meant avoiding the Anglia Helicopter Corridor, never an issue and they were only just outside Conningsby. Additionally, the ac were operating closer to good radar heads with better low level coverage.
Helicopter Corridor is the way forward! When I used to be an FC, low level traffic that we couldnt see was always a concern. We might only be giving a FIS at that height, but as mentioned in other threads, DoC is always at the front of your mind.