Thanks Darren onced again. I was really confused so I sent email to Philippine Embassy in London.
I am glad to share with you and to other members.
Here's their reply:
Yes, your Philippine passport becomes invalid when you obtain UK citizenship.
However you can then apply for Dual Citizenship (form downloadable from Embassy website) and at the same time apply for a new Philippine passport.
Please note that you have to go to the Philippine Embassy in London to swear your Oath of Allegiance before being granted Dual Citizenship because you lose your Philippine status when ever you get UK passport.
Please look at the section on Dual Citizenship on the Embassy website for more information of the requirements.
Regards
Thank you very much.