An in-line pipe inspection tool has one or more inspection platforms (28, 30) which are connected to an elongate wheeled trolley by link arms (20 to 26). The trolley unit (10, 12) has drive means for driving the point of connection of the first link arm (20, 22) to the trolley (10) relative to the point of connection of the second link arm (24, 26) to the trolley (12), thereby to move the inspection platforms (28, 30) in a direction perpendicular to the direction of elongation of the trolley (10, 12). Thus the inspection platforms (28, 30) are movable which is relative to the trolley (10, 12) to permit the tool to be adapted to pipelines of different diameters. Moreover, the platforms (28, 30) preferably have permanent magnets which contain a rotatable magnet. The rotatable magnet permits the net magnetic field generated by the platform to be varied.