how does the "customs airfield" thing work from, say, Abbeville? Abbeville is deemed to be a customs airfield for arriving in France if sufficient notice is given. So, after visiting the town you decide to fly back to the UK......... is it still a customs airfield for the return flight?
Yes, but still 4 HR PNR to AD operator or by fax to Customs. In practice, they are pretty relaxed about a/c departing to the UK, so if you turn up from Blois, for example, it will only take as long as it takes to process the FPL.