Double you may think there are stringent restrictions on the way SN money is used - indeed, there may be restrictions - but these are ignored and bypassed on a daily basis. Many - I hesitate to say most, but I believe it is most - use SN budget to employ TAs who help with the whole classroom, fill in for teachers, do admin, etc. Very few children with funded 1-1 support get the equivalent amount of time on a 1-1 basis.
When my DS moved into primary 2 in his last school they only had a TA to support the reading groups (so a whole class activity), despite my DS having 5 hours a week of funding. The HT told me his funding was going into primary 1 'where there were some real issues this year.' I don't doubt that there were real issues, but using DS funding to support those issues was fraudulent IMO.
Schools do have a vested interest in keeping children on SN lists. Which is actually hilarious when you see how hard they push to stop your child from getting onto 'the list' in the first place.