Ici I take your point on LBRUT being at the "least worst" end of the spectrum but I know of children with SEN across the country still waiting for offers. How to make them feel even more different even as their friends are excitedly planning their next step.
However FYI here is the government code of practise on the process every other Council is supposed to follow to be lawful www.gov.uk/government/uploads/system/uploads/attachment_data/file/398815/SEND_Code_of_Practice_January_2015.pdf
In particular " "Where the local authority considers a particular mainstream place to be incompatible with the efficient education of others it must demonstrate, in relation to maintained nursery schools, mainstream schools or mainstream post-16 institutions in its area taken as a whole, that there are no reasonable steps that it, or the school or college, could take to prevent that incompatibility."
So the LA would have needed to get similarly worded letters from other mainstream schools, some as I highlighted before like Orleans that have specialist units and experience, before it could lawfully place the child at Clarendon.
As the mother of a child with SEN I am quite sure any mother sending a child to a newly established school would be asking a lot of careful questions. We have plenty of experience on which to base cynicism. Believe me if Turing are true to what they say is their intention on SEN and are going to give all their teachers training so that they truly understand the brain differences and needs and adapt the teaching in the course of every lesson then they will have gone the extra mile over practically every school, state or private, in the borough. You are happy if there is just a SENCO in place who is not of the "well intentioned and cuddly but woolly" school - a term coined by the Disability Assessor in Kingston, and perhaps one or two teachers who really get your child and go the extra mile to develop their confidence and achieve their potential in the course of an education that otherwise leaves them reliant on their own coping strategies. Mostly teachers either have no real insight or, actively misunderstand. I have heard many similar experiences at schools across the borough.