Actually mum I was mostly commenting on primary /prep level. Most of the selective secondary's around here do aim to be inclusive and do not seem to discriminate in selection, and that is apparent in the proportions of pupils at the schools getting diagnosis and support. It was a question I asked for obvious reasons and at most it is about 10% which since that is the incidence in the whole population points to them being inclusive and being effective in identifying difficulties. The support when pupils get diagnosed is patchy but Hampton and Latymer Upper even have state of the art centres of excellence, drop in centres where pupils can access support and equipment such as Kindles, and I also know a pupil who is getting exceptional individual support at Westminster.
The stated intention for the selection process of most schools is to focus on ability rather than attainment /tutoring so if they are successful in that then you would expect them to select around 10% who are either already diagnosed (and almost all give extra time in the entrance exams to those with a diagnosis) or will be diagnosed at a later stage. An emphasis on reasoning papers in the entrance process (Wimbledon High are now selecting purely on reasoning papers, as the Tiffins used to, though the latter use pretty poor quality ones that appear to be tutorable), which are actually used by Ed Psychs as part of the diagnostic process to determine the ability of those with SpLDs, is particularly inclusive. As are the exams for the more selective schools that try to test lateral thinking and logic skills. And most schools know the difference between an accurate answer that does not show much evidence of intellectual skills and one full of silly errors (or even misread) that does.
Obviously there is a level of disability where these sorts of school would not be able to provide the level of support needed, and in any case would provide a confidence sapping environment so to that extent they discriminate but plenty of bright pupils with SpLDs get selected and can and do do well at these secondary schools.
I don't know the situation at Radnor but the only independent school that I know of that does not aim to be inclusive is Ibstock, the Head there makes it quite clear to new parents, presumably part of her strategy for getting the school up the league tables, but she is a notable exception.
LBRUT is known for having relatively good strategies for addressing the issue at Secondary level with specialist units and quite a few pupils being transported and having fees paid for specialist schools like More House. Though relatively good is probably still leaving a lot of pupils who achieve above average levels in spite of their difficulties without the support that would enable them to achieve their greater potential. That is certainly a common complaint I have heard from the Helen Arkyll centre (incidentally a fantastic resource for local parents www.arkellcentre.org.uk )
I am of course oblivious to bad grammar 