I've only got my phone for the Internet at the moment, and with Mudcat's current instability on that, I can't expect to contribute much to long threads. Will try again tomorrow at the library.

A "mock" according to the AUP Scots Dictionary is one of the tiny non-viable eggs hens sometimes lay. Brilliant image in the context. But it's a local usage, mainly West Lothian. The song is a weird mixture of stuff like that, which has to have originated in Scotland, and generic ballad-mongering that could have been written anywhere.