Yes, you'll need a WWCC (Volunteer or Employee) before you go on placement. The turnaround time for this is a few weeks but i'd get it done ASAP so you're well prepared to go out on placements. They usually ask for you to apply for a WWCC early because placements are organised well in advance - and this helps with the planning process.
In terms of a criminal record / police check, this is not needed because the WWCC covers your legal requirements to enter a school. The Volunteer WWCC is free and is all you need, because you are not an employee of the placement school.
You don't have to have it before you start your course - but you need to be aware of uni deadlines for when they want you to get it by. Like I said, the turnaround time is usually a few weeks so you would want to do it at least a month before your first placement.
Let me know if you have any other questions, i'm doing the Master of Teaching. Send me a PM or something, to keep this thread on topic. Thanks