An electromagnetically operated switching device comprises an armature (82,102) having a magnetisable and moveable portion (82b,102b) for displacement between two stable rest positions. Two pole pieces (60,62) are disposed on opposite sides of the armature. The pole pieces form poles of opposing polarity adjacent to the armature, and the armature is magnetically attracted to a respective pole piece in each of its stable rest positions. A coil (54) is arranged to polarise the moveable portion of the armature when the coil is energised, such that the moveable portion of the armature is displaced from one stable rest position to the other by energising the coil so as to polarise the portion to the opposite polarity to the adjacent pole piece. Each pole piece (60,62) comprises a permanent magnet (68,70) with the permanent magnets disposed on opposite sides of the moveable portion (82b,102b) of the armature (82,102). The device may be configured to control the flow of fluids.