Posted this as a possible conclusion to this thread
Following is a practical example of my experience of a BiLateral Visa Waiver Agreement entry/exit to the Schengen Area. Answers the main outstanding premise of this thread, ie I found it possible to exercise this right with a positive outcome, but with a few caveat emptors👍👎
My recent exercising of the 'Bi-Lateral (New Zealand) Schengen Area Waiver Agreement on a winter trip to Spain via France and how it went.
Departure : 26th Nov. '23 presented UK Passport at Newhaven. On entry to France at Dieppe showed NZ Passport, this was stamped. Explained to Customs official that I intended to exit France on the NZ Passport via the NZ/France BLVWA. He didn't have any knowledge on what I was on about, amicable wave through however.
I then went to the terminal hoping to find a clued up official, armed with a handful of supporting documentation, no one on duty, only a couple of daily sailings NH/Dieppe so not entirely unexpected.
Apparently Dieppe are sans specific Immigration Personnel. Customs perform double duties, mild surprise.
Return : Well before the Dieppe ferry boarding time I went to the terminal, the staff on duty had no knowledge of BLVWAs. They were however a helpful friendly bunch, and sent an email copy of my NZ Passport to Immigration HQ Paris? A few hours later a return to the terminal confirmed a positive Paris response. Went through the Immigration control booth, NZ Passport was duly stamped 16th March. (111 days in Schengen Area). Showed UK Passport on entry at UK Immigration Newhaven.
Despite my positive experience, I think that due to the lack of official knowledge regarding BLVWAs, it could be that my next trip may be viewed and interpreted in a different light .......ie negatively.
Calais of course does have an Immigration contingent, they should be fully conversant on the Rules and Regs. Which may/not prove to be a positive thing.