Thanks - interesting to read those details. Do you mind me asking when the 18 vehicle formation travelling you mention you did was? Would that have been in the 1960s or did that remain into say the early 70s?
I travelled on the night Dunkerque service three times in 1974, once in 1975 and twice in 1980.
The 1985 book 'Night Ferry' by George Behrend and Gary Buchanan reports the seated portion ceased to be attached to the Night Ferry in 1975 and thereafter was provided by an EMU - and by 1980 it was in it's final months so my journeys would have been in 1974 and possibly 1975 also.
The book also notes twelve Mk1 vehicles - 2 x BCK, 2 x CK, 3 x TSO 3 x RB, 2 x RUO - were allocated to the Night Ferry workings (including maintenance spares etc), and fitted with UIC ETH plus there was one additional BCK available with UIC ETH. The RUOs had gangways on one end adapted to couple to the sleepers. In the latter years as stated, only the BCK was conveyed, the restaurant facility having been withdrawn in the intervening years, by then also with an adapted gangway.
The formation on my 18 vehicle workings hauled by a class 71 departing Victoria was from the loco BCK, 2 x CK, RB, 2 x TSO, (locked gangway doors) RB, RUO, 7 x WL type F, 3 x SNCF vans (which conveyed mails), five WL for Paris and 2 for Brussels.
The aforementioned book notes the Brussels sleeper(s) were marshalled between the Paris sleepers and the vans (which all went to Paris) so obviously some remarshalling took place as they came off the ferry at Dunkerque to have them at one end of the train for detachment during the Lille reversal.
For a period in the 1960s a sleeper for Basel was also conveyed, also detached at Lille together with the seated vehicles from Dunkerque to Basel and Milano (which got there well into the evening)- I recall travelling on that portion which was one of I think three trains in the day (the other two from Calais) routed via Charleville-Meziers and Metz and onwards through Strasbourg and Mulhouse.
Boarding at Victoria seated and sleeper passengers were segregated as those in the sleepers passed through UK passport control which foot passengers encountered at Dover , hence the need to lock the gangway doors between the seated and sleeper portions of the train and with a physical barrier on the platform.