Ledsled,
All you can think of is that the IFR clearance is not available because of conflicting traffic (having told us that you can't have E without radar) ---- but it is beyond your imagination that, just perhaps, the most common problem is that the centre frequency is not available on the ground.
You keep lambasting me for being insular, no real "world" experience and stuck inside the 12nm limit, so I have question for you: the number of times you have taken an RPT jet out of a CTAF into low-level E would be?