SD158 Restrictions on Flying

I am being lazy here. I have come across numerous references to the flying restrictions imposed on training aircraft from the start of WW2 via the publication SD158. The restrictions seem to involve minimum heights and areas of restricted flying, mainly in the East of England where enemy activity was deemed to be the greatest and therefore Fighter Command and the defence Radars needed to keep to a minimum the numbers of training aircraft buzzing around so they could detect potential enemy aircraft more effectively. The various reference seem to have contradictory elements which I assume to be revised rules leading to an eventual relaxation at some point.

As this had a direct impact on the use of ranges, particularly air to air firing areas I wondered if anyone had researched this and had a handy summary of what restrictions were in force and when changes were made?

Also restrictions flying to and from certain aircraft factory airfields when barrage balloons were flying such as Weston-super-Mare which was restricted to Bristol AC / ATA pilots within certain corridors - everyone else was banned!.

The apparent contradictions I am finding I assume are to do with relaxation of some rules over time and the eventually removal of most of the countrywide restrictions at some point (1942/3?). Also differences the between day and night restrictions. And then there is the "Grantham Line" and bomber lanes which also seem to be mentioned a lot. I also suspect the slow installation of IFF in training aircraft and particularly target towing aircraft also had an impact.

It's sounding like this is a whole subject in itself but it may also explain a few decisions made regarding ranges - I think!

I need a drink!

I have been delving into the files on the this subject to find reasons why ranges fell out of use around 1940. Leysdown and Chesil ranges appear to have "closed for the duration" in the early part of the war as they were deemed to be in operational areas and training aircraft would add to the radar plots and make it difficult to identify enemy aircraft. It was also suspected that copies of the "Most Secret" SD158(part2) - a map of danger areas, ranges especially, may have fallen into enemy hands at the fall of France and those ranges would offer easy targets for prowling Luftwaffe fighters. From the airfield point of view it implied that the restrictions caused Ford to be released by the FAA to be an operational base and there was mention that the same fate might have affected Yeovilton, but I suspect exceptions had to be made.

I have not seen this aspect of air defence really mentioned in any text books but I know it seriously hampered navigational training and night flying training and may have caused many units to move north and west (Warmwell B&GS to Dumfries?).

Has anyone come across references to the subject in any books as it seems to be a complicated and changing subject that had far reaching implications in the early war years but I am reluctant to get diverted away from my main research to take it any further. Maybe in a few years if nothing has been written on the subject