Who decides what treatment / care to offer?

This is up to professional assessment of needs, clinical appropriateness and, inevitably, competing demands for finite resources.  An adult patient with mental capacity to make all their own decisions cannot require a particular treatment or care package to be offered by the NHS or social care – it is not their decision to make.  A child or adult who lacks capacity for some decisions does not get any preferential treatment in resource allocation.  If you want to challenge a decision not to offer a particular treatment / care package you should take legal advice about seeking judicial review of that decision.

If treatment / a care package is being offered, or there is more than one option being offered, then a decision must be made by, or for, the patient whether to accept or refuse, or which option to take.

If a patient cannot make their own decision then a best interests decision must be made.

Best interests decisions are choices among the options available, on behalf of someone who cannot make that decision for themselves; they are not about offering different options than would be available to anyone else in the same situation.