Two points about that. I've always associated George Galloway with that phrase but does anyone know if it is his originally or was he quoting someone?

He certainly popularised it. I'd heard it before here but not in a party political context and I think Galloway claimed to have got it from a Scottish woman at a demonstration he was at which would fit.
Another visually evocative favourite of mine in the same scurrilous vein used to describe a ludicrous pretentious person somewhat Ill-suited to their job/ task is "A Coo with a gun...":