Usually when you have your appointment someone will go through your application form step-by-step and question-by-question. They will not only check that you have completed the form correctly, but they will also check that you have supplied adequate and sufficient supporting documents/evidence etc.
Photocopies will be made there and then and the originals will be handed back to you.
Hopefully not too much has changed since we did ours.
Others will be along soon to add their own experiences
Like Joe says it makes no difference that your Philippine passport has expired.
And yes once photocopied they will give it back to you.
Be aware that if UKBA need your original passport they can request it from you