If you hold a UK driving license and wish to drive in the Philippines, then it is the law that you hold a International Driving Permit, along with a valid driving license. This applies to driving in most countries abroad.
These IDP's are valid for one year, and you can have them pre-dated. They cost just £5.50 at post offices that deal with them which to be honest, is not really that many. You also need a recent passport picture, so that's another fiver.
For those who are lazy like me, you can use the AA site, and do it by post. They only want photocopies of the original required documents, and the charge is just the £5.50 + £3 admin, so not bad.
Apply well in advance of leaving on your holiday or fiancée meeting.
