Engage an independent consultant to examine and cost the reinstatement of former railways which connected Exeter with Newton Abbot and Plymouth, and which provided diversionary routes when the line through Dawlish was closed.
Why is this important?
No amount of money spent on the coastal route will make it invulnerable and arguably some of what the fantastic schemes being proposed would cost should be spent on route diversity.
Rail passengers will accept being diverted in an emergency because they remain at their seats and know how much longer their journeys will take.
The danger is that far too much money will be spent on the coastal route and that vastly better resilience than it has now will never be achieved. With worsening conditions, it is possible that no real progress will be made and all the while there will have been no attempt to create route diversity, once a great strength of the British railway system.
Short of tunnelling behind the cliffs, no amount of work will make this route invulnerable: it only needs to fail in one place to stop trains. As was said after the Dawlish débâcle in 2014: "The challenge is to ensure that the existing line has the greatest possible resilience, but to have readily available an inland diversionary route between Exeter and Newton Abbot."