@sofia A necessary condition is consent yes.
As far as I can tell, Ellerman is not an anarchist, but his democratic theory is still useful to anarchists and I would recommend reading it. Ellerman's notion of democracy isn't something that just applies to the state. For anarchists, democracy is the only legitmate way to make collective decisions when people have to come together in organizations and communities.
It does makes more sense to consider anarchy the sovereignty of none.