What I find issue with is during times of employment when for example the OPs husband was a high earner, OP was probably getting far more CMS that required to live comfortably and actually able to save some money, there were peaks and troughs here.
The payment was reviewed in April, to a reasonable level of £1.1K / month (a % of his salary plus an adjustment for the number of nights he is supposed to have them). I received that in April and May, and the payments will continue through the summer (i.e. three months of his notice period). It looks very flush, but in reality does not cover 50% of childcare fees (I have a 2.5 yo and a 4 yo, and have to pay for two full time nursery places in London). No savings, but April and May were first months where I did not have to add to my debt / credit cards, and it REALLY made a difference to how I feel about my life.
OP - what do you think of the idea of 50/50 care?
He won't do it, and we both know it. He does not even have overnights now, accepts he does not have the skills or patience. Maybe it will be an option when they are older and a little bit more manageable.
OP, but have you thought about writing to your MP at some point?
I don't really want it to become too public. I even never told anyone from my friends, everyone thinks (knowing that ex had a good career) that we are well supported. I name changed on here as well.
Oh come on, yes it's abhorrent he's not paying for his children's upkeep - but taking on a 6 year slog of studying cannot be the driver to avoid paying the OP. (Plus she's referred to it as previously being a dream of ex-DH)
I don't think he is doing it specifically to avoid maintenance, there are easier ways of doing that. Yes, it was his dream - but on the other hand, he has quite an idealistic view of what medicine is. When we were still together, I asked why does not he go to train and volunteer with St Johns Ambulance / Red Cross / etc., but that was too primitive and boring for him. He is quite bright academically and I don't have a doubt that he is able to do the course - but as many of you, I am sceptical that he will see it through because of the sheer work pressure.
We’re you married OP? You say Ex rather than exDP
How has he run up debts in £150K salary?
Yes, married but for a very short time. He does not have debts, it is me who is a bit drowning in them 
@TooTrusting
Thank you so much - a lot of very useful information and I will definitely spend a couple of hours this weekend researching about it. Yes, we were married and there is a financial order in place (silent on the child maintenance as at the time ex was temporary unemployed and in the process of moving abroad).
Does he have many "dreams"?
Quite a few. Ironically, the children were his dream once too.
How often does he see your children? Is he planning on using his time studying to see them more?
About once every two to three weeks, for a couple of hours. I doubt he will see them more, as his university is quite far away from where we live.
Anyway, I have no useful advice other than to note that a friend whose course family member did the dirty to her financially felt better after turning the whole sordid episode into a murder mystery. It was a decent book, too!
Actually, my "dream" is writing a book that I've been pregnant with for at least a decade.