lingle - the diagnostic/ assessment stuff would have to be completed for a statement.
to qualify that - not every child with a statement will have a diagnosis, but to get a statement they will have to have been assessed by the relevant professionals... iyswim...
statement of special educational need details the help that the child needs in the education setting (and which setting) - in order to get a statement there is a statutory assessment process carried out by the LEA, but they request reports from parents, current setting if appropriate, as well as every man and his (professional) dog that the child sees/ may need to see/ thought necessary by paed - so physio, OT, slt, social services, camhs, any as/asd outreach workers, specialist teacher advisors etc etc etc etc.
so you don't need a dx to get a statement, but if you aren't keen on assessment per se, it makes the whole process even more difficult...
assume it is the label rather than the recognition of actual difficulty you have declined? declining assessment would be tricksy from a stat assessment pov i think...
parent's report essentially is one of the reports looked at by the case officer. history from birth, developmental/ milestones/ current difficulties etc as well as providing a list of all the people that the dc currently sees (so that they can request up to date reports from them)
without a statement you are very much at the mercy of the education setting as to what support the dc will get. some schools are absolutely fine and manage to provide, but some struggle and will request ed psych and stat assess in any case.