How to apply for a Partner/Spouse Visa Under New Rules

Why do I need a UK birth certificate? He doesn't need that to get british citizenship or for his Filipino passport. In the future, he can get that from somewhere in UK, I'm sure since he's a registered British citizen

Yes, that's a possibility, a DNA test. The British never used to ask for that though, I know from other European countries anyway. He will just have to get that if required.
Sorry about that and your ex partner.

I think I'm correct in saying that Ian would have to fly to Manila and have his sample taken at the same lab and at the same time as his son's. That lab is, of course, one specified by the UK authorities and will certainly not be the cheapest.

Yes, a DNA test is possible. I am prepared for that. They are not so expensive I think

It doesn't mention any dna tests on gov.uk application process.

No he won't. If you believe that he may need a Birth Certificate, for whatever reason, then the only way you will get anything remotely resembling such a document is by registering his birth with the British Embassy in Manila. But you are strongly advised (and would be so advised by Consular staff) to obtain his British Passport first.

That's not compulsory, I thought. It's just reassuring for certain parents. But it's not necessary, that's what I read

That's not necessary, I read It's just to reassure certain parents

He only needs a Filipino passport and a UK travel visa to travel, he already has a Filipino passport. Of course he needs a UK tourist visa. I will think about that though. Will I get problems from UK passport control if I am with a filipino baby without his mother? Didn't think of that, but that's why I came on here, brainstorming.
That wasn't my original plan, however

I can't afford that, you've got me there unfortunately

Good point. Yes. I must get him a British passport and a Filipino passport to get out and mother must come with us through Philippines passport control or get the paperwork from DSWD

If it is your intention to bring him into the UK on a tourist visa and for him then to remain here, you should dismiss that idea from your mind. You are throwing up all sorts of red flags here. Firstly you almost certainly won't be able to board a plane alone with him in the Philippines and should you arrive in the UK without the mother, you risk having the child removed and placed into care as you be deemed to be too old to care for a young child.

At the risk of repeating myself, you/your girlfriend need to obtain the following in the order shown:

1. Philippine Passport
2. British Passport
3. (Optional) Certificate of notification of Birth Abroad

The first two, the Passports, need to be applied for as early as possible.