Hi Rob
I was based in Saumur a couple of years
Normally, flying from or to the Channel islands not a problem, provided you inform police or customs 2 days before (working days )
Contact the CCI Chambre de Commerce et de l'Industrie, who is more or less in charge of this.
Prepare a form with pax & crew details (passport numbers... ) arrival & departing dates and try to stick to ETA & ETD .
There is a good chance you will meet police on departure or arrival, just for a documents check and that's it .
I no longer have Saumur CCI contact details, but you should easily find it in Pooleys, Jepp's or Bottlang .
Unfortunately, Dominique, who was the AFIS over there, is no longer in charge. He was a precious help for all pilots coming there .
I have heard Saumur will close soon or later ... what a pity . Such a nice place, such a nice airport .
As there is no longer AFIS, you should normally use auto-information ,in french.
No big deal if you get the standards procedures translated before.
Watch out for nuclear power plants in the Loire valley . Plenty of them and strictly forbidden to overfly .
Enjoy your flight, and feel free to contact me if you have any question
Nicolas