Hi Dave,
Generally never, which is why I say the entire UK is an active LFA & you need to keep an eye and ear open for any traffic. Heli's and Prop's aren't too much issue as you can hear them coming a long way off (esp. Chinooks!), but jets are a bigger worry with their speed.
There are regular corridors that mil traffic use, some are official and marked as such, others are there simply because it's a popular/regular way in/out of an area. I live under one such corridor that feeds traffic between the Newcastle CTA and Spadeadam DA & RA's - general mil traffic routing North South can bypass Newcastle via the North Sea or go through what's known as the Hexham Gap - a narrow strip of class G airspace where they don't need to contact Newcatle tower or Spade Control. If exercises are under way in the north sea, then they'll often route via the gap to avoid the exercise area, if exercises are under way at Spade or Otterburn then the gap is often used by exercise aircraft to route in/out and by other non-exercise mil traffic at the same time.
The lakes is a popular low flying area for mil traffic (guess they enjoy the sceneray and the thrill
) - Traffic through the lakes often takes the routing I mentioned in a reply above - they go over the Dales to the north of Leeds CTA and can head for Kendal area and then via various Lake district valleys northwards. Sometimes they head on into Morecambe Bay, or to Galloway, or call in to Spadeadam for EW stuff. They then head back south to Yorks or Lincs either back thru the lakes, via the Durham dales, or via Hexam Gap. Dunmail Raise is a popular spot for aviation 'togs to photograph low flying traffic. It's a bit like the Mach Loop in N Wales.
The only times I've noticed where a specific notam regarding low flying is issued is when an exercise is taking place (eg Joint Warrior), or there's a forward control exercise in a localised area. Then, it's not about low flying, it's about AIAA's. Typically, the notams are really quiet this week, so I can't give you a specific link, but here's a link giving a general idea of what they're about...
Forward Control Air Exercises - I've 3 such areas within 20-30 miles.
Basically, my experience is that the RAF (and friends) can and do fly low level anywhere and everywhere in the UK so the idea of specific low flying areas is a bit academic really.
If you know you've a job on and you're going to be malingering at 300-400ft in one area in the hills for a while, yes it'd probably be wise to call in and let the low level booking cell know a day or so before, then they can include you as a hazzard in the briefs - but they won't exclude your operating area and you can still have traffic through at low level, so you always need to keep that lookout. I've recently seen some amateur footage (think it was on youtube) from France or Belguim i think) that shows a mil jet passing underneath the drone - that's something I never want to happen to me
