Can parents give consent for the living arrangements of older teenagers who cannot give consent themselves?

When a child aged 16 or 17 lacks capacity to consent to their living arrangements, what happens when they are placed in local authority residential care? Can a parent consent on their behalf? If they can then there is no need for the local authority to seek judicial authority for the placement. If there is no consent then Article 5(1) would be invoked as this would constitute deprivation of liberty.

We work to make sure equality and human rights standards are respected by the rules and practice governing entry into, exit from and treatment in institutions. 

We intervened in the case using our powers under section 30 of the Equality Act 2006.

We intervened in this case, arguing that placing D in confinement was depriving them of their liberty.  The Court agreed and held by a majority that parents cannot consent to the confinement of a 16/17 year old child, even if they lack capacity to consent for themselves.

Very shortly after the hearing the Government wrote to the Court to inform them they were amending the Mental Capacity (Amendment) Bill (now the MC(A)Act 2019) which was passing through Parliament, to extend Deprivation of Liberty Safeguards to 16/17 year olds.  

While this was pre-judgment it appears likely that the appeal influenced this amendment and it therefore had significant practical impact.