Thanks for all the support... I'm pretty sure I've done the right thing for me. It's a big step, but I've plenty of contacts who I can start to hit for work, and the MD of the company I work for (who to be fair has always been really really supportive - although sadly not that involved day-to-day any more) has said that he, personally will be keen to continue to work with me on a freelance basis... Which was nice and also useful!
Do I think they deliberately worked me out? No, don't think so, but they certainly didn't go out if their way to make the three day thing work well either. Not malicious, I don't think just shortsighted, disorganised and a bit lazy.
And don't get me wrong, I didn't expect the same level of responsibility that I had before, especially with regard to managing others... However, my strengths have always lain in ideas generation, problem solving and creative direction, and I had a baby, not a labotomy, last time I checked...
Seriously, whenever I have contributed in these ways I know I've delivered and then some, so I honestly can't understand why they won't use me more in this capacity, which seems infinitely compatible with a three day week...
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Especially since I'm actually in the studio more than many if the other senior creatives who spend much of their time in internal management meetings, doing people's reviews and stuff...
But look, I get a bit riled when I think about it, but honestly, with two kids, commuting, a house to run and a husband who works A LOT I honestly don't have the energy or the appetite for a big fight about it.
Surveys have been done, and there's a reason there are hardly any women over 35 in creative roles in the industry, I guess...
Thomas, you may not be me, you may make different decisions about part time/full time work or you may end up at a less busy, more organised or more enlightened agency. I can't find your thread - what's the title?
And if you do find yourself in my position then pm me - I might be in the market for a great freelance working mum, who's been undervalued by her employer and wants to use her talents on her own terms... 
And my friend wasn't trying to make me feel bad, she's a working mum too, and gas been through the same difficulties, and left a previous position for similar reasons, regretted it, and is cross on my behalf that I'm in the same position, that's all. She's not trying to make me feel bad, she's encouraging me to fight, but understands why I'm not.
I really hope the freelance thing works out or I'm really stuffed...
Good to hear it working for so many though. Perhaps it's the future... 
db
xx