Please have a read down this page to an article written by Prof Alfred Baird:

A ferry, Scotland to Europe

Alfred Baird was, prior to his retirement in 2016, Professor of Maritime Business and Director of the Maritime Research Group at Edinburgh Napier University. He has a PhD in Strategic Management in Global Shipping. His specialist area of research and teaching is strategic management in maritime transport.

In the article, he states "The severe supply chain constraints now facing Scotland as a consequence of Brexit means that a direct ferry service is no longer simply ‘nice to have’ but is now essential to meet the future trading and tourism needs of the Scottish economy."  He says it much more succinctly than I did!