Saturday evening Eurostar Marseille/London have crossing a standard double deck TGV. That's the good picture to compare Eurostar trainset which have exactly same length as 2 coupled TGVs. The specificity of Eurostar versus TGVs consist of two independent "half-sets" each with its own locomotive/power car. The cut is visible above of the banister (right of the track) where it is clear that there are 2 bogies between the central cars while there is only one between others cars. In the event of a serious fire on board while travelling through the tunnel, passengers would be transferred into the undamaged half of the train, which would then be detached and driven out of the tunnel to safety. If the undamaged part were the rear half of the train, this would be driven by the "Chef du Train", who is a fully authorised driver and occupies the rear driving cab while the train travels through the tunnel for this purpose; Source Wikipedia.
