LEA is the Local Education Authority.
If he is on School Action Plus, he should already be being supported via regular IEPs, drawn up and agreed with you, with achievable targets for him set down. School Action Plus, also requires him to have contact with external professionals, such as an Educational Psychologist or Inclusion/ASD support worker or teacher.
According to the last site I linked to, the school don't actually have to provide IEPs, but they do have to have keep records of the support they are providing in order for his education to be properly 'inclusive' and for him to meet his targets.
"Sometimes the school will not write an IEP but will record how they are meeting your child's needs in a different way, perhaps as part of their lesson plans. But they should always be able to tell you how they are helping your child and what progress they are making."
If you feel ganged up on, you could try contacting your Local Authority's Parent Partnership who will come to meetings with you. They are able to mediate and can be really useful, as they know how the system works and what the school should be providing for your ds. Its worth bearing in mind though, that they are funded by the Local Educational Authority, so are not completely impartial - although they are supposed to be.
I never attend school meetings alone. There's strength in numbers and it helps for one person to be able to take notes, while the other gets stuck and tries to sort out the problems.
If he has a diagnosis already, I would definitely be going down the Statementing route if I were you. The school cannot choose to not support your ds or differentiate for his Special Educational Needs and by obtaining a statement you would be making sure that they are legally bound to support him properly.
You don't need the school to apply for a statement, you can contact your Council's Local Education Authority yourself and make a parental request for statutory assessment. The process is explained in the DirectGov link I posted in my last post.
The link that Attila, posted is excellent for helping you get through the statementing process Ipsea and SoS SEN is another great place for information and support on SEN issues and statementing.
Ultimately though, if you don't feel the school is providing the proper support for your ds, is there any way you could move him to a different school? It seems crazy, given that they have a unit for SENs, that they are failing to support a child with a clear cut ASD diagnosis, but if they are being so obstructive to properly supporting him (probably because their SEN budget is already over-stretched - but that's absolutely no excuse) moving him to a different school may be the best option.