There is a legal responsibility to house anyone who becomes unintentionally homeless or is in priority need. There isn’t though any right to compel those who are voluntarily homeless to accept housing. There is just a duty to offer help in finding accommodation.
Tent cities bring their own problems. They demand facilities to be provided, water, sanitation and waste disposal. Most of all they would be ok in the summer months, as an emergency provision, but not in the winter.
I have worked in the past for Shelterbox, a local charity who provide tents and equipment to areas around the world struck by disasters. When buildings have been destroyed these can provide emergency shelter for a month or two, but getting people into more substantial accommodation is always the priority.
So whilst it could help an unexpected surge during reasonable weather it’s not an answer to the underlying problem.