Dr. Andrea Mulligan:

It is very difficult on the travel question. If we consider the analogy with the termination of pregnancy, it was necessary to insert a specific right to travel to access abortion services.

There is at least an argument that there is an entitlement to stop someone going abroad to end a life, for example. There is probably tacit acceptance that it is quite different from going abroad to take drugs in a jurisdiction where that is legal. It is a tricky question of constitutional and criminal law and how they interact.