http://www.dcsf.gov.uk/
you can get the Schools Admissions Code of Practice and the Schools Admission Appeals Code of Practice.
If your child has been refused a place on infant class size grounds (ie on the basis that by the end of the year the total number in the class will exceed 30 - the law states that there can only be 30 pupils in Yr R or Yr 1 without the school having to take qualifying measures), the only grounds on which you can appeal are that 1) there has been some mal administration and 2) that the education authority has made a decision that no reasonable education authority would make - something along the lines of splitting up twins. Distance from school, spliting up siblings etc does not equate to unreasonableness.