Sorry, I realised about an hour ago that I had missed out this important information. It's 49 cm. Here's the full spec.
Headset: Acros AZX-220, tapered, block lock
Seatpost: Satori Trident
Seatclamp: Kalloy SC-201, 40,0 mm
Tyres: Schwalbe Super Moto-X 62-584 Reflex
Rims: Alex MD40, 27,5"...