I must say that I find this post very interesting.

This may end up being a rather long post

On the subject of dual citizenship I wish it were possible to clearly state a definitive successful strategy, but it’s not. Eventually there are just too many gray areas to consider

There is however a recognized legal process to apply for naturalization in the Philippines.
The major qualifications include:-
Must not be less than 21 yrs of age
10 years continuous residence (5 years if married to Phil citizen)
Must be of good moral character and believe in the principles underlying the Philippine Constitution, and must have conducted themselves in a proper and irreproachable manner during the entire period of residence in the Philippines in his relation with the constituted government as well as with the community in which he is living.
Ability to read and write English or Spanish AND any one of the principal Philippine languages
Must have enrolled minor children of school age, in any of the public schools or private schools recognized by the Office of Private Education of the Philippines, where the Philippine history, government and civics are taught or prescribed as part of the school curriculum, during the entire period of the residence in the Philippines required of them prior to the hearing of the petition for naturalization as Philippine citizen.

Always remember it is a judge reviewing all of your qualifications that makes the final decision. Whether you meet all the requirements or not, the judge makes the decision. You might meet all the official requirements but because the judge doesn’t think you've integrated enough into the local Philippine culture, he turns you down. The same is true the other way; you might not speak a major Philippine dialect fluently, but you brought solid upstanding Filipino citizens as character witnesses who speak glorious words about your contributions and character and the judge lets you have citizenship.

Additionally, there are some costs/fees involved. I do not know how much these would likely be at the end.
Timescales are about 3 years (initial application 1 year before petition, final decision not less than 2 years after filing petition)

It is not necessarily the case that you give up British Citizenship.
British nationality can be renounced by a declaration made to the Home Secretary. A person ceases to be a British national on the date that the declaration of renunciation is registered by the Home Secretary. If a declaration is registered in the expectation of acquiring another citizenship, but one is not acquired within six months of the registration, it does not take effect and the person is considered to have remained a British national.
Renunciations made to other authorities are invalid.
Prior to receiving the Philippine naturalisation certificate you must declare in open court that you renounce absolutely and forever all allegiance and fidelity to any foreign prince, potentate, state or sovereignty.
Under international law, the Master Nationality Rule says that a State may not give diplomatic protection to one of its nationals in a country whose citizenship that person also holds. For example, if a person is both British national and Philippine national, he cannot be given diplomatic help by a British Consul in the Philippines.

Furthermore, the state issuing naturalisation also has the legal power of cancellation.
Anyone obtaining naturalisation fraudulently will be subject to a fine or imprisonment or both and cancellation of naturalisation. (probably after the term of imprisonment so that any other diplomatic service cannot help you)

By the way I’m not an expert or a lawyer if anyone knows something is incorrect please share.

Terpe