The parent governor concerned can't resist interfering. If it's someone who will teach his child he becomes frantic. We've now had a row over an exclusion, where quite exceptionally the committee of three overturned the school's decision. We were unanimous that the evidence against the boy was insufficient and largely hearsay. Our new colleague's daughter had been a victim in the saga of the excluded boy and he's given us all a roasting for our decision.
YOUR colleague's behaviour, though well-intentioned, is really destructive in a case lik the exclusion. It is so much easier to deal with such issues in the abstract, which is why I'm so keen on governing bodies setting aside some time to remind themselves of their working-together principles.
Among these, corporate responsibility, trust in groups to whom a task is delegated, no recriminations once a decision is properly made, should be paramount. Your chair or some other experienced and respected governor must talk your colleague through these matters. He will soon realise that no governor would lightly overturn the head's decision in a case like this. Give him time to learn. In the end his intense interest could be a great strength.