Whoops, reposted as looks like my internet had a problem.

Some more on section 13(a) permanent residency.

You have a choice on whether to apply in the UK or whether to apply when you're in the Philippines.
Personally I believe the section 13(a) has some benefits (apart from the ability to leave the country an re-enter without an exit-ticket)

For a number of reasons I wasn't able to secure my 13(a) before departing for the Philippines.
So I entered under BB privilege and made my application for conversion to 13(a) whilst living here.
Means I needed to secure all the mandatory legalised documents for my application before leaving the UK
Take a look at the Philippines BI website for details on how to apply.

Alternatively you can apply for 13(a) at the Philippine Embassy London. Take a look at their website for requirements.