I've picked up a copy of 'Special Educational Needs and the Law' by Simon Oliver.
OK, it's as dry as it sounds, but it's really very useful
I got it from Amazon at £32. It's pricey but it has a wealth of information and I figured it would save hanging on the phone to IPSEA or checking things with my solicitor. You might be able to request it at your library.
It seems to be aimed at advice workers/lawyers rather than parents, but I found it quite accessible and would recommend it for anyone heading towards tribunal, especially for those doing the bulk of the work themselves.
It goes over the SEN COP, tribunal regulations, complaints and the system in Scotland, Wales and NI as well as England.
It expands upon and interprets the information in the SEN COP and tribunal regs using case law references and examples (the author is a barrister and SEND chairman).
The only criticism I'd have is that it was published in 2007 so it doesn't take into account the newer SEND regulations which changed in 2008. But most of the legal arguments are still valid.