There is no specific requirement for Learning support teachers to student ratios I am afraid. It does depend on the needs of the pupils and whether or not the pupils have an EHCP and the real need for the support. For example 1:1 support, interventions etc.
Please let me know how many pupils in the class and if any of them have an EHCP ? This will help me to possibly give a deeper answer if need be.
Hope this helps!