Passengers travelling from Brussels-Midi to Lille-Europe on Eurostar trains are not subject to U.K. Border control checks at Brussels-Midi, nor are they required to go through Schengen exit controls as they are traveling within the Schengen area.
They are however required to pass through security checks in a dedicated Intra-Schengen terminal at Brussels-Midi.
In addition these passengers are asked to board coach 16 (e320) or 18 (e300/TMST) which is segregated from the remainder of the train.
This is to ensure passengers who are travelling on an Intra-Schengen journey do not remain in the train bound for the UK without having gone through UK Border control checks and Schengen exit checks. On arrival in Lille-Europe, all Intra-Schengen passengers must disembark from this coach and exit from the platform.
In order to do this we have to section off coach 16/18 on the train to allow these passengers to travel.
Unfortunately our systems cannot differentiate between the coach that is reserved for the Intra-Schengen passengers and the rest of the coaches for passengers travelling to the UK. This means that sometimes on the GDS it will show there is availability, however the segment will then come back unconfirmed due to these seats being reserved for these passengers.
A space is only confirmed on the train once seats have come back from Eurostar (9f) and the segment is also confirmed. If no seating has come back from Eurostar (9f) even if the sector is confirmed the ticket is not guaranteed.
We advise agents not to guarantee a passenger that they have been booked on a certain train until that confirmed sector and seating comes back to the agent. Please check availability in a separate PNR and not in the same booking as we cannot reinstate an original ticket.