British passport, expired phil passport...returning to London after long stay in p.i

[jokerevo]

Was there any reference to the British passport stamped in his Filipino passport on entry? Such as foreign passport presented?
Does he have the original or copy of his naturalisation certificate?
ACR card is not an issue. He entered on a Filipino passport.
What is the real issue here? He is worried about leaving to return to UK on his British passport as he was not stamped in on that one?
If he has been here for nine years then his British passport will be almost expired.
Whats the problem with renewing his Filipino passport and using that to travel to UK.
He can show the airline his British passport or even better his Naturalisation certificate no need for visa etc
He can obtain dual citizenship in Philippines if he has not already done this. BI website has details.
What am I missing here? Seems a simple problem with a simple solution.

The concern is he will exit with the BRIT passport and present an expired Phil passport which he will be fined for and perhaps be prevented from leaving.

He is now in the process of renewing the passport but I was curious as to the potential fine value as we are trying to get him home asap.

The British passport would be the preferred choice as it is still valid. I perhaps failed to state the urgency of the need to travel.