Right, so a school that has a blanket policy of denying is potentially not following the applicable legislation. This is the kind of thing that a judicial review decides - whether public bodies are making decisions in a lawful manner or not.
As far as I know, every LEA that has had such a blanket policy on this has been found to be acting unlawfully when taken to tribunal. This is why so many LEAs that used to be obstructive have now changed their policies and in most you now simply tick a box if you wish to defer.
It seems secondary Heads haven't yet caught up with legislation a decade old (!) but after a spate of tribunals again the same will happen I expect and they'll realise they have to comply with the law not make decisions based on their personal preferences/ prejudices. One would hope that this time it will happen faster because if they refer to the LEA for advice on the matter the LEA should already be aware that Heads cannot choose to refuse to admit children in the cohort they have been in throughout primary school, having dealt with deferred primary admissions for years now. Academies, being their own LEA, may take longer to get the message hammered home.
Again, all of this would be avoided if there was a robust regulator in the education sector ensuring all schools and Local Authorities comply with the law rather than leaving it to parents to force them to do so through tribunals, as with SEN provision.
Perhaps a judicial review on both of those would be helpful to prevent thousands of parents having to raise individual tribunal cases constantly to force schools/ LAs to act in a legally compliant manner. The education system is a shambles.
And no, to address PP's assertion that only people who are not academic/ failed at school hold this dim view of schools, that doesn't apply to me at all. I was a straight A student at GCSE and A level (no thanks to my many, almost all useless schools) and have a degree and professional qualification. But thanks for implying I'm not intelligent because I have experienced how appallingly schools behave. It's precisely because I value education that I've had conflict with the school system^^ because I would like my children to actually be able to have the support at school for their disabilities to which they are legally entitled so that they can reach their academic potential, and not end up with trashed mental health in the process.