So I emailed National Rail last night about travelling via the ECML to see what they would say out of pure interest and got this load of rubbish back this morning
Dear Chris
Thank you for your email about the Rail & Sail.
There is a Rail & Sail to Belfast and Ireland. This ticket offers an all in one ticket for rail (from any Scottish station), coach link (between Ayr and Cairnryan) and ferry travel to Belfast (via Cairnryan) with Stena Line.
Rail & Sail Anytime Single tickets are only valid for the ferry crossing shown on the ticket and are subject to availability based on ferry capacity. Regrettably, we have very limited information about these tickets and hence I suggest you contact your retailer for specific information. Rail & Sail are available for sale at Stena Line telesales on 08705 455 455.
Alternatively, you can contact the Telesales department for ScotRail on 08457 55 00 33 for more details.
Thank you again for contacting us.
Regards
Customer Relations Executive
National Rail Enquiries