Dutyholder is the umbrella term for the parties who carry legal duties on a construction project: the client, designers, contractors, and the principal designer and principal contractor. The Building Safety Act aligned the building regulations dutyholders with the long-standing CDM roles.
Each dutyholder must be competent, cooperate and share information, and keep the records their role requires. Crucially these duties apply to ordinary building work, so a small contractor doing notifiable work is a dutyholder with real obligations, not a bystander to a regime meant only for tower blocks.
The common thread is evidence. A dutyholder is expected to be able to show competence, decisions and what was built, which is exactly the record that disorganised projects fail to produce.