Quote Originally Posted by acs View Post
... you will still need to pay the fee if you over stay the 21 days period.
A tourist visa will allow you to stay for up to 59 days. A non-visa national (that includes Brits) can visit for up to 21 days without a visa. In either case, the length of your stay can be extended, two months at a time, for up to two years, by visiting BI, completing the forms and paying the fees (3,020 pesos for the initial extension).

The only problem with this is that, officially, you're supposed to have your return flight booked when you arrive. I understand that Manila immigration do normally check this, but in my four arrivals this has never been asked for at Davao.