The Union idea is excellent AbbeyA, I should have thought of it. Most are very temp friendly these days.
Personally, I'd adress the complaint to the head of the school or LEA, however I would word it very very gently and nicely as you don't want to risk a name as a trouble maker.
It's difficult to say without the full compaint, but IIP, ISO, all of those sorts of 'badges' don't actually hold much sway if there is a complaint, rather that they insist a procedure is in place. BERR is worth the trawl. If you find the grounds, they will put SELECT through a remarkably longwinded process of having to justify themselves, which also involves a government rep coming to see them and taking the complaint up. Even if you don't win it's nice to think you've given someone there a days worth of arse ache for your troubles.
SELECT is a large company made up of many divisions, and to be brutally honest, you're probably going to waste at least, if not more time than I did blowing smoke. The problem with making a stand in these sorts of matters is that they just don't care. And they have a market that they have fairly much cornered so your value to them is negligible. My experience is that they have absolutely no problem at all ill advised comments 'by accident' that can through a persons, or companies reputation into free fall. Hilariously for me, they came crawling to me cap in hand (i run an agency) because of the specialists I supply, but I'd be surprised if you get far.
Please feel free to let me know the whole complaint, I'm qualified in employment law, and have much expereince with SELECT. But much as I like a moan, unless they owe you money, I'd probably just resort to the old baby poo in the post thing ()