IO,
I wouldn't be very famalier where my flight plan goes when I lodge it, so I'll bow to your knowledge on that one
Having said that all I can say is that in my experience I've never been refused a transit, and I allways lodge a flight plan in advance. Others have been refused who tried to lodge it while airborne. Maybe I'm just lucky.
In practice transits are not a big deal, as it's very easy to avoid controlled airspace here, with the exception of eastbound departures from Weston. Unless you need to fly closer than 10 miles to one of the regionals you can usually decend below controlled airspace without much hassle.
Most of Ireland is covered by Class G, so I wouldn't get too hung up on transits.
As for arrivals & departures from controlled fields, just don't bother trying to do it without lodging your flight plan 60 minutes in advance. You're only creating hassle for yourself and everyone else on frequency. You're unlikely to be allowed to depart. You might get someone nice, and be able to talk your way into an arrival claiming you'd already lodged it, but I wouldn't bank on it.
I know this doesn't answer your specific question, but it's as much as I can tell you.
So don't get hung up on transits. They aren't particularly important given all that Class G. But always file 60 minutes before take off for departures/arrivals to controlled files.
FNG,
The goose is severly underused! Rarely moves!
Let me know when you guys come over, and we might try meet up for a drink.
dp
ps. FNG.....what is FNG an acronym for?