I've found dayuse to be limited in its offering of hotels with a focus on the central corridor North of the river. It seems so many of the establishments in London just don't offer day occupancy and therefore aren't plugged into this service.
Haven't been able to find any other sites that offer a better selection or localised focus.
Airbnb also not much use.
Tried calling hotels direct and asking if they have day rates, no joy with Travelodge or PremierInn