Thank you for your replies and experiences. Much appreciated! I'm sorry for those in similar situations :-(
I received an email today with his 'better' suggestion.
He wants me to home school the kids or send them to a free school at the other side of the county (I don't drive ergo he has total control) , I'm not against home schooling but as a single parent this is impossible financially as IS would stop once both children hit school age presumably. I'm not on IS as I have a p/t job but I actually couldn't afford not to be in F/t employment when children are of school age. I feel strongly that I need to build a career of some sort so I can provide for the children so being at home is just not a viable option.
He doesn't work (odd jobs here abs there since dc born but usually fired or walks out pretty quickly) and has always been financially abusive (even now deducts money from maint if I do not do as he says ) so I suspect this is actually about me needing to rely on him for either school pick ups or financially as I wouldn't be working.
He wouldn't h/s as he doesn't cope that well with both the children, has untreated and years old mental health issues, and to be honest he has never committed to anything in his entire life (two failed degrees, walked out on and has barely provided for two children) so I couldn't trust him with our children's education anyway.
We've been discussing preschool since April so him suddenly finding a alternative on the day DS begins is laughable and total reflection of him just attempting to blockade this at the last minute and throw his PR weight around. He try's to stop us on every PR right and argues black if I suggest white every time there's a discussion involving DC 
DS loved his session today :-) totally thrived! I'm so so proud! And he can't wait to go back. I'm only starting him on two sessions a week so ex argument of me abandoning our son to a fundamentally flawed education system is pretty out there. Apparently I'm following the flock as I always do and not working in DS' best interest
DS asked to go to school, what lesson would I be teaching DS if I didn't listen and act upon his perfectly reasonable request. I'm child led in pretty much everything and want my children to know I love and respect their views.
Preschool are on side and said they would support DS in whatever way they can.
So stressful
has massive anxiety that he was going to physically stop us going today which was tough. Tried so hard to mask it from he children but they are little emotion sponges aren't they so they were on edge for a while this morning. I wish with all my heart I wasn't putting them through this.