The AGNI’s argument was that the subjective element of deprivation of liberty – “lack of valid consent” – has an autonomous ECHR meaning, and so you can give valid consent to confinement despite lacking the relevant MCA capacity. This consent would mean there is no Article 5 deprivation of liberty. The charities argued that the two are effectively the same (which is what we had all assumed before thinking about it).
The following article Revisiting Cheshire West by Dr Lucy Series has some interesting arguments in favour of revisiting our understanding of ‘valid consent’ but ‘provided there are adequate safeguards’ (begins halfway through the article).