The invention provides a wind turbine blade body manufacturing method, the method comprising the steps of: providing a mould (40) having an elongated mould surface (43), placing a movable insert (50) on the mould surface, in a first position, forming, with the insert in the first position, a first blade body having a first length (L1), placing the insert (50) on the mould surface, in a second position, and forming, with the insert in the second position, a second blade body having a second length (L2) which is different from the first length.