Elsa was in the same situation last year. From memory, you need to print the SPA from the Philippine Embassy website, sign it and then it needs to be counter signed and stamped by a local solicitor or "Commissioner Of Oaths", try Francis and Co in Welsh St, Chepstow (I have dealings with these people). Then the FCO in London has to stamp and validate it (I think its free?), as the document was signed in the UK, and only then can it be sent to the Philippine Embassy for processing by their own lawyers.
I used to live in Caldicot by the way, not far from sunny Chepstow.