I believe It is quite common with some blues, mainly older ones in thier 40s and older, it is just usual city self deprications, just like rags songs like this is how it feels and city are a massive club were turned around to mock them then so was the use of berts as a thing they used to take the piss.
Things they used to mock us for, curly watts, peter swales, frank sidebottom ete, mamaging to fuck up are nostalgically looked at and rather than being used by them anymore to takethe piss by many who refer to themselves as berts
Some blues use the term, a lot of others probably don't.