There is always a member of slt there generally the head
That is a clear breach of the Appeals Code.
Paragraph 2.13 is clear that representatives of the school may not support individual appeals. It sounds like the head is indicating which children they want admitted. The Appeals Code clearly and unambiguously tells appeal panels they must not allow this to happen.
Paragraph 2.15 is clear that at no point should anyone representing the school be in the hearing with the panel unless the parents appealing are also present. Whilst that only covers the hearing, it should go without saying that when the appeal panel makes its decisions the only people present should be the members of the panel and the clerk. Neither the head nor any other member of the school leadership team has any business being there. Having them there jeopardises the independence of the appeal panel. The importance of the appeal panel being independent is emphasised several times in the Code. If parents involved in unsuccessful appeals find out that someone representing the school was present when the appeal panel was making its decision that would be grounds for having the decision overturned.
Yes, the school will be involved in the appeal. A representative of the school will present the case to refuse admission and answer questions from the parents. They are entitled to question the appellants after they have put their case. They will also sum up the case to refuse admission near the end of the hearing. That is the only involvement the school is allowed to have in the process.
This isn't a case of "doing things differently here". This is a case of blatant disregard for the Appeals Code. The Appeals Code is a statutory code so it has the force of law and can be enforced by the courts if necessary. If this isn't sorted and a parent finds out it could be very costly for the school. I strongly suggest you read the Code and make sure these abuses stop.
Just to be clear, I am not blaming you for this. I suspect from your responses that this was going on long before you joined the appeal panel and no-one has ever told you it is wrong. But it is wrong and it needs to stop.
Getting it fixed may not be easy if the school has managed to house train all the other panelists. But it must be fixed.