Improvements relating to wind turbine blade manufacture A method of making wind turbine blades of variable length is described. The method involves forming first and second half shells of a main blade section in a main blade mould assembly. A pre-manufactured tip section is selected from a plurality of tip sections of different lengths according to a total length requirement for the wind turbine blade. The tip section is supported adjacent to the main blade mould assembly such that an inboard end of the tip section overlaps with an outboard end of one of the half shells of the main blade section. The main mould assembly is then closed to bond the two main half shells together and to bond the tip section to the main blade half shells. The invention allows blades of different overall length to be produced using a common main blade mould assembly.