The duty to carried out an assessment as to whether a person is in need of support services arises under Section 9 of the Care Act 2010 which provides
Where it appears to a local authority that an adult may have needs for care and support, the authority must assess—
(a)whether the adult does have needs for care and support, and
(b)if the adult does, what those needs are.
A similar duty in relation to assess whether a carer has a need for support arises under Section 10 of the Act