there is a good reason not to keep the filipino passport (making a bit of an assumption here I know..).
basically if you are caught in a natural disaster, war, or something less serious (say you stole a car & were getting the death penalty
) the UK government would not help you if you had a fil passport.
If you had
only a brit passport then the embassy in theory at least will help you escape, or stop you from getting
.
there are lots of other plusses and minuses of course... but I know there are several people on the forum who have a background of nicking cars