would i need a visa to transit to the philippines via saudi if travelling on a british passport?

I cannot see why you would want to do that. Saudi airlines and saudi airports are not to be recommended.

Fill in visit Visa on entry to Philippines. Pay on exit

you are aloud to stay upto 1 month on a visa...if you overstay...immigration with try and extort money from you when you try and leave phil. immigration officials are very corrupt here.. i would only transact with the officials in the philippine embassay in london... i know from experience when i sorted out my visa...