Some people do want to make this complicated.
Firstly there is a big difference between phoning up to land at a private strip, that might have difficult approaches, livestock on the runway etc, to getting PPR for landing at a licensed airfield.
For the private strip then you will generally phone in advance, except those, quite a few, which say, dont bother to phone, you are welcome any time. And if you have phoned up and the farmer has said he will have to move the sheep etc, then if you are not going to go, then you might phone back to save him the trouble. But if he has said yes, come in any time, we are open all day, someone might be here, then if you decide not to go, no problem.
But if its a licensed airfield, where the Notams dont show any closure, then unless its PPR by phone, there is absolutely no point in phoning up, particularly if youve been before. And if you do phone up for PPR, then you are asking for Permission to land there, not booking a slot. So if you have permission and dont go, then no problem, you still have permission but just didnt go! No point in wasting more of their time with another phonecall.
If I have booked a slot then yes phone back to say I wont be using it, so someone esle can have it, but how often do you need to get a slot! except for fly-ins at North Weald.
If Im going out flying for the day, I might look up the fields in the flight guide the day before and phone up any requiring PPR by phone the day before to get permission, but Ive no idea when I might get there- sometime in the afternoon. So its a bit stupid to rely on me being there at a certain time. Of course if they say its closed between 2 and 3 for a display or something, then I'll make sure Im not there at that time.
Other days I might just fly somewhere and from there decide to go somewhere else, if it says PPR by phone, then hard luck, as I probably wont have a phone with me, and there might not be one where I am, but otherwise I can just look the place up in the guide and go.
As for the flightplan system, it seems to work fine to me. Lets not increase the bureaucracy. There is no need at all to file VFR flightplans unless going abroad, lets keep it that way! We dont want to go the way of Spain, where you need one for every flight and can open and close them in the air, but only if you can actually get hold of someone to hear you!
Re Flightplans, I also cant see the point of needing them when going from one Shennegen country to another, as you dont need customs and immigration now!