Edit 12/7: Went to On Your Bike to arrange for a test ride only to discover the smallest size they have - 47cm comes with 700c wheels. The member of staff even trawled the website for me. Trek do a smaller size, 43cm which I'm guessing is the one with the smaller wheels, so I've emailed them for clarification.
Trek 1.2 WSD comes with 650c wheels.
Edit 12/7: Went to On Your Bike to arrange for a test ride only to discover the smallest size they have - 47cm comes with 700c wheels. The member of staff even trawled the website for me. Trek do a smaller size, 43cm which I'm guessing is the one with the smaller wheels, so I've emailed them for clarification.
Will report back.