Healthwatch England has compiled information on how people who are homeless can access healthcare

Homeless people have the same rights to register with a Doctor as everyone else – even if they have no permanent address or proof of address
NHS guidelines say that GP services cannot refuse to register someone because they are homeless, do not have proof of address or identification, or because of their immigration status.

GP surgeries can only refuse to register someone if they are already full or if the person is living outside the practice area – and they must explain this in writing.

Healthwatch England – Helping someone who is homeless access healthcare