cag I second getting a copy of the flexible working policy before he starts asking/ gets in his application
If he's in a union take a rep/ workplace colleague to his meeting. And insist on a note taker if the policy allows.
If his employer doesn't follow their own policy e.g. Doesn't hold a meeting, then that will give him grounds to appeal so he gets two chances at it.
He will need to be given business reasons if the request is turned down.
There's normally a time limit to responding to these requests.
A bit of flexibility on both sides may make him more successful.
I had a flexible working request granted on appeal (no meeting was held). And I've recently as a manager helped my member of staff get a flexible working request through. She originally had no hope as the pattern was unworkable, but coming up with a more realistic working pattern helped immensely.
Sorry had a long day so can't remember much on the thread. Feel better soon copper