Most people I know have done the masters part time over 2 years so they could continue working as they are mainly in their 20’s/30s with kids having returned to education and retrained as teachers. They’ve obviously change training requirements since I explored doing it myself before lockdown (I wonder if this might possibly be because they were struggling to recruit people into training and the shortage of staff was worsening 🤔).
And even if/although this has changed it still doesn’t affect the fact that it will take several years to provide a significant number of SEN staff when there is already a shortage - of both existing SENs and qualified teachers interested in transitioning into it. My DD was given a IEP in 2015, my DS did/does have a ECHP. Had I known my post would be forensically parsed I would have clarified. The point is that it is hard in many areas to get one without taking the LEA to court. I live near a specialist private school for boys - 60% are LEA funded, many after taking the LEA to court - and they are all placed in that school because the local state school do not have the staff or the resources.
And with respect to the rest of your post, I think you are being disingenuous. There is a current teaching shortage because of both staff retention and failure to recruit. New graduates are leaving university with £45k+ of student finance debt. They are seeking jobs where they have earning potential so they can pay this off. Teaching salaries (and working conditions) do not attract them when weighted against this.
Private schools will not be generating 20% tax on current fee income - as many as 10% of students will leave; other schools will lower their fees to offset the 20% increase; others (like my children’s) will combine lowering fees with offsetting VAT due against increasing other estate income, such as wedding and event income etc. Once they become registered for VAT it means they can also claim back VAT charged on purchases/expenditure - so all the goods and services they buy in which charge VAT they can now offset against the VAT they charge on fees. Most private schools anticipate the net VAT owed will be approx 7-8%. So the govt will likely generate less than 40% of the revenue they are anticipating. The government are utter idiots for not appreciating that they will not be scooping 20% VAT on fees, because of the offset. Any builder, plasterer or plumber can explain this impact.
The government may plan to put some of this (now much reduced) revenue into additional SEN provision, but as I’ve stated it is already woeful, hence many parents having moved their kids into the private sector. And where, due to the length of days and access to free after school ECAs until 6pm, they are more able to take full time jobs (I and other mothers have done this to pay for it); these parents, now at the mercy of state school hours may no longer be able to work full-time in new schools, meaning less income tax revenue. And this is assuming there are places at local state schools - they are all over-subscribed in my area so new applicants often wait years for places and join a waiting list that is double digit long for each year, albeit it those with ECHPs will go to the top of that list… again shunting kids from poorer families without access to private assessments further down the list, but hey, it’s about an equal and fair system, right?
The system is broken, with decades of underfunding and provision is overstretched to the point of being non-existent in many areas, even if not in yours. It will be vulnerable children from families who cannot afford to get private assessments who will miss out. These are often children with parents equally challenged by ND/SEN and having been failed by the education system in earlier generations and less able to advocate for them. Labour, through sheer spite and ideology, will ultimately hurt the most vulnerable children in our society by their shortsightedness - so who cares if a few privately-funded, vulnerable children get caught in the crosshairs on the way down?