Thank you everyone - I appreciate your help.
I have no idea what that 'fakeroad' entry is either, but it's clear that it is not needed by Richard's packs, so I shall rule that out. Many thanks for the help on that. Anyway, in case it should throw light on any item common to all the failing routes, here are the packs and their results...
AP1 Variety: scenarios stored in London - Oxford route
Everything works perfectly! Wonderful scenarios too!
AP4 Passenger: scenarios stored in Newcastle - York route
Two scenarios fail: King's Cross - Darlington; Plymouth - Aberdeen
All others work perfectly.
AP5 Freight (also Newcastle - York)
Failures: Stockton - Cardiff Tidal; Carlisle Yard - Tees Yard; Tees Yard - Carlisle Yard; DRAX PT1 and DRAX PT2
Only two scenarios load.
Other possible factors:
I'm using Vista 64-bit ('nuff said)
My game is installed on a different drive and path from that used by default
The game is the UK edition updated to MK2, and I have all the official add-on packs that contain any scenarios
The only 'patch' I have is the modified cabview of the Deltic (a miracle patch I adore)
On install of Richard's routes, my IOW route kindly decided to remove itself. I hadn't backed up the Routes.xml file so I ereinstalled the IOW pack.
RS_Tools mentions that my only missing item is that fakeroad_3.bin item which is not connected with Richard's packs. All stock is present for Richard's scenarios, including the fixed class 43s.
I deleted my Blueprints.pak file
I do have a few other custom scenarios, namely Downhill Tankers, Checking the Island Line, Clearing The Line (Paddington) downloaded from here, and some JustTrain scenarios that came with the Voyager (and the required stock to run all these - oh, and a Hymek which I love but have no idea what to do with because I've never edited a scenario!). In fact, looking at my 'other factors' above, it's probably a wonder anything runs!
Thanks acorncomputer for the link. I've never used the scenario editor before so this should be a baptism of fire! I will give this a go to see if it provides clues on why my game is being such a toad!