Well in that case I don't know why he was allowed to get airbourne from LGW. We were told that he was refused landing permission at LHR when on the ground at LGW and as far as we knew he was off to Stansted (strange I know!), but he did then divert in due fuel!
Plus, the captain is the final arbiter in making any decision regarding his flight. So, this means if LGW do indeed refuse him take-off clearance he can still get airbourne anyhow - I am pretty sure this didn't happen here but this is an extreme example!