peatair.
The rules for the low-level route are a typical mish-mash of figures and requirements that were written may years ago and have been 'adapted' to the airspace as it is now. I couldn't tell you when the LLR was established, but it was certainly in existence in 1970. At that time the whole Manchester CTR was 'rule 21' airspace, (Class A as it would be now). Regarding wether you can use it in the northern section and comply with rule 5 I think the best answer to that is included in the briefing I linked too in the earlier post. When I'm flying I definately would not fly over the centre of Warrington but go around on the East side. I'm quite happy with the rest of the route provided a little care is taken as I feel I can safely fly at such a height that would enable me to alight clear of a built up area in the event of engine failure. There was some discussion some years back about changing the max altitude in the northern portion and possibly changing some of the rules but for practical reasons it was decided that the LLR worked best as it was. Wether that will be so in future is another matter! By the way, I can remember seeing an RAF Vulcan using it around 1971!! Wouldn't want to meet that coming the other way!!
Spiney
P.S. I've just looked at your profile and see you're a retired ATCO so you'll know all about Rule 21! Probably seen a few Vulcans go through the route yourself!