You will always be a Filipino first and foremost if you wish to, that's a fantastic thing about this country is it's respect for diversity, this oath thing is just ceremonial to perhaps show you accept/embrace/respect a British way of life etc, I wouldn't worry about it, it doesn't make you either less Filipino or more British, I think of myself as English not British, definitely not european but still hold a UK passport. Wish I could get an English one.
