Hi,
I am indeed in Essex.
DS was originally dx'd with developmental delay and speech and language delay. ADOS threw up a couple of autistic traits as well; none of that surprised me really and it does not change who he is.
Always seek independent advice from organisation like IPSEA, SOS:SEN, ACE, Network 81 etc rather than just using Parent Partnership. Use the net; it is a valuable resource. IPSEA have good letters you can use and adapt. Also make full use of this particular section on MN; I was not on MN at the time but if I had been it would have been most beneficial.
DS has had a Statement from Y1 (five years ago now) and has done well on the extra support given to him. His statement was both specified and quantified in terms of support offered; that is very important because once you agree to the Statement proper it is damn nigh impossible to get it rewritten.
What we did at the time was apply directly to the Chief Education Officer at the LEA in question following IPSEA's advice. Gave them six weeks to apply, LEA of course say nyet to Statutory Assessment. Throwed that crass decision back at them and arranged a meting to negociate (we only did this because we thought they would do a u-turn based on all the evidence given). Turns out the panel threw it out originally due to lack of evidence from school - threw nice but firm wobbly at school and they then put all their papers in. SA gets granted!.
The above is a very condensed version of what transpired and does not go at all into any emotional pressures we were all under at the time. I feel still somewhat scarred by the whole thing and I still dread the annual reviews that having a statement entails.
Do not give up the fight, you are your child's best - and only - advocate.
HTH