The letter should tell you how to respond. Since they are asking for a police clearance, it would need to be regular mail.
It's not technically a PPR, but I would include the PPR along with a note - here is my passport to help expedite processing. Generally if they are asking for a new police clearance, they are ready to issue PPR after they get the clearance.
You may also want to include proof of financial support. This is something new some VOs are asking for when they do PPR. (Ottawa and London for sure.) You can send in paystubs, tax assessments, savings, etc. I sent in copies of my husband's paystubs, another copy of his employer letter (to show same employer), and a screenshot of our savings account. If you aren't sure if your VO does this, check with the thread dedicated to your VO.