UK licence is valid for 90 days. There is no need for a International Driving Permit to legally drive in Philippines. It may be a necessary documentary requirement with some car hire companies.
Philippine driving licence is valid for 3 years and it is a legal requirement to carry it when driving.
I do not know any expats here who carry their original passport or ACR card. A xerox copy is acceptable.
As Fred rightly states many policemen and enforcers do not know the law,this is especially true concerning foreign drivers licence regulations
