SEND ratios are purely down to whether children have funded EHCPs that give them 1:1 time. Otherwise it's just normal ratios regardless - 1:30 in KS1 and no ratios in KS2.
That said, I've had KS1 classes over the past couple of years where the unsupported SEND and emotional/behavioural levels meant it was unsafe in my classroom physically, with children attacking other children and adults, throwing things, leaving the classroom etc Often children had just about coped in EYFS with a completely play-based curriculum, lots of free choice and more adults, and EHCP assessments had been started but were slow-going and these children found the transition to KS1 very tricky, despite my best efforts to provide individual support packages and continuous provision etc I have ended up constantly calling SLT/Head to support as I had to remove the rest of the class, and I had conversations every day clearly stating that I couldn't keep the children safe and that learning was being constantly disrupted. I recorded everything, and sent emails/CPOMS daily so that it was all recorded officially.
I am lucky to be in a school where they trust my judgement/experience and listened to me, and it meant lots of additional work with the SENCO fast-tracking support and assessments, bringing in extra adults and getting lots of very complex systems in place to support children. But it has been VERY tough at times, and I've doubted my abilities as a teacher and have been very stressed. In the last 3 years I've had 4 children coming through the class who had no support initially, but were transferred to Special Schools by the end of the year, one with a 2:1 ratio needed, and 5 more who got 1:1 EHCPs. And I don't think my experience is unusual at the moment.