Your landlord must make sure your home is fit for human habitation. If you are living in poor or dangerous conditions that mean it is not safe for you to live in your home then it could be classed as uninhabitable.
Some examples of problems that could mean your rental home is uninhabitable include:
Structural issues that make the property unstable
Severe damp and mould problems that could cause health issues
Not enough natural light
Poor ventilation
Water supply issues
No heating