Hard to say if it will be good or bad, certainly it will be educational, enlightening, and maturing for you. If I were you, I would. (now being much older, considering the idea in retrospect, wishing I had thought of it at your age)
Do not go if you are not able to handle yourself and have some street smarts, ie: if you can't hang out or survive in the rough areas in the UK, don't think about going to the Philippines.
Due to your age, you need to realize that you will be a target for thieves and scammers, including girls who may want to play an extortion or false rape accusation against you, it is common, so be very careful, and always check the ID and age of any girl who you intend to be alone with. It is a crime to be in the same hotel room alone with an underage girl, if there is a presumption that some sort of illicit sex could occur, and this law is often used against nieve foriegners.
Many folks in the philippines are poor, and most earn less than 1 UK pound per day.. you can easily find drinking buddies if you are the one buying the beers.. The girls can be great, but beware that there is a great cultural difference from the UK, many girls are marriage minded, and want to date, but won't want to have sex, and will regard any dating or courting as signals of your intentions to marry.. viginity is still prized, and protected by the family, so you could get into huge trouble on what you may regard a casual date, they may regard as an irrevocable commitment. The upside to the dating ritual is that it is sort of OK for a guy to fool around and date 'party girls' while courting his 'true love' (a ritual that could take a long time). So it is different from the UK where kids basically screw around, at some point pair off as bf/gf, then maybe marry.. in Philippines, traditionally, guys generally don't think about marriage to same sort of girls they fool around with... they are sort of a seperate group.. if that makes any sense?.. so don't confuse dating with courting, and don't confuse your date either.
To play it safe, if you are decided on going alone, stay at a nice hotel or resort, where they will screen guests and provide security.. and for casual dating upscale go go bars are a safe bet because of the low chance of being the victem of a scammer. At 18, the go go girls will just love you, and you will be pleasantly surprised how sweet, charming, polite, modest and dianty they are (compared to typical UK chicks into the dating/club/player scene) . If your intentions are honorable, you can just mingle and let your aquaintences know you are looking for a gf, and you will likely be introduced to available cousins, nieghbors, etc.. The malls are a magnet for good looking girls, a great place to find them, IMHO.