I think that was shorthand for there aren't many residential moorings in general and not many will be available.
More liveaboards probably live under the radar on non-residential moorings. Pros - cheaper, no council tax Cons- no official address, worries about living outside of your agreement, usually no car parking etc.
Do a search on this site. There are lots of topics on this.
Aquavista have residential berths at White Bear Marina near Chorley and Galgate near Lancaster, probably elsewhere, but you have to enquire for availability and cost. Other marinas may also offer residential moorings.
https://www.aquavista.com/mooring-options/residential-moorings