Unfortunately by the time I got home (with a side trip to Meadowhall) I'd forgotten about the beer bottle. I've no idea why I remembered about the beer a few weeks ago, but I did, and so I set off to try and find some. It turns out that it is indeed called Flying Scotsman and is brewed by the Caledonian Brewery in Edinburgh. As I couldn't find any local shops selling it I settled for using the breweries mail order website to order eight 500ml bottles.
Given the picture on the label I was fairly certain that it was being brewed in relation to Flying Scotsman the locomotive, rather than the route from London to Edinburgh, and the label bears out this assumption:
Introducing Caledonian Flying Scotsman Premium Bitter which has been specially brewed to celebrate the return of the world's most famous locomotive after a major restoration programme at the National Railway Museum in York. Salute the loco with a glass of this superb beer. The finest barley from the north and robust southern hops combine to produce a full flavoured beer. Look for a raisin-like spiciness and a superb toasty dryness. Caledonian Flying Scotsman -- First Class refreshment from Edinburgh to London and beyond.I can now reliably inform you all that it is an excellent beer; as the label says, it is indeed a First Class Refreshment!