I probably wouldn’t advise involving parents, but you could call the current school, and possibly any authority advisors/agencies named on the document. If you have a good relationship with the SEN Officer, you could also talk to them.
The reasons for refusal, as you are probably aware are:
• It would be unsuitable for the age, ability, aptitude or SEN of the child or young person, or
• The attendance of the child or young person there would be incompatible with the efficient education of others, or the efficient use of resources
If you can clearly evidence these, this would be your grounds for saying no.
Use the document to match the needs/provisions to your evidence as to why it would be detrimental for the young person and/or the other students.
To be honest, funding might not be the best focus as all schools have a duty to meet needs – and Advisors should be available for you to make referrals.