There are legitimate reasons other than appeals for admitting children above PAN.
A new Code is due next year, but the current
situation is set out here.http://www.elevenplusexams.co.uk/appeal ... -school#c6
If schools were to admit above PAN in breach of the rules, they would be answerable to the LA or DfE as appropriate.
One possible consequence is that, in any subsequent appeals where the school is resisting the admission of further children, the appeal panel might be less than sympathetic to the school's case!
I think it unlikely that there would be any consequence for a child admitted in the circumstances you describe.http://www.elevenplusexams.co.uk/appeal ... school#c16