a magnetiser for a pipeline inspection tool . the magnetiser comprises a ferromagnetic base member , a pair of driving magnets mounted at spatially separate locations on the base member and a flux enhancing magnet mounted on the base member adjacent to one or both of the driving magnets . the directions of magnetisation of the pair of driving magnets extend in opposite senses to each other , towards and away from the base member respectively to create a magnetic circuit that includes a flux path between the driving magnets which passes through the base member . the flux enhancing magnet has a direction of magnetisation substantially aligned with the direction of magnetic flux on the flux path , the flux enhancing magnet being magnetically coupled to the adjacent driving magnets to drive flux around the magnetic circuit and thereby enhance the magnitude of a magnetic field exhibited by the magnetic circuit outside the magnetiser .