I've spent almost a year dealing with Admissions for my particular dilemma and only just been told about my county's Education Entitlement Service. I think they are like the last chance saloon. They've been very positive anyway.
I'll update in a week or so when I hear back from them.
But just to say, if you are having problems with In Year Admission for Year 1 or 2, dig about amd see if your county has one of these teams, you never know.