With all due respect LI, seems to me you're Trapped inside the Project for the Old UK Century. Going forward, that model is never going to work again. IMHO, like.
Something along the lines of what happened to the Liberals in the Eighties when they joined forces with the Social Democrats to form the Lib Dems. Labour will have to form an alliance with the SNP at some point if they want to remain a force north and south of the border.