Assuming your tour was post 2002 (when the tunnel re-opened after the fire disaster in 1999)....
Were your group allowed through & permitted to bunch up - or required to maintain a constant (& monitored) low speed, and a large constant distance between your vehicle and the one ahead?
If you were allowed to bunch up in a train - then the tunnel has had its safety rules relaxed considerably from when we used it.
No restrictions at all both times I've used it (the first in 2002, I didn't build the car until 2001). Due to never growing up (why else would you choose to use a 2 seater with little storage space to tour Europe for 2 weeks) there was quite a lot of acceleration and deceleration to make silly noises