An anti-theft device for a vehicle which includes a power plant and a drivetrain, the power plant being drivingly connected to the drivetrain in order to propel the vehicle, the anti-theft device having an unlocked state, a locked state and a priority locked state, characterized in that the anti-theft device includes: a locking member which is mounted adjacent to the drivetrain, downstream of the power plant, and which is movable relative to the drivetrain between an open position, in which the anti-theft device is in its unlocked state, and in which a driveshaft or transmission of the drivetrain is permitted to rotate freely; and an engaged or locked position, in which the locking member prevents displacement of the driveshaft or transmission by locking it in position thus immobilising the vehicle; an actuator which is configured to displace the locking member from one of its open or locked positions to the other; an electronic control unit which is communicatively linked to the actuator in order to control actuation of the actuator, the electronic control unit also being configured to receive a motion signal indicative of movement of the vehicle; and at least one wireless communication module which is communicatively linked to the electronic control unit and is configured wirelessly to receive signals from first and second remote control devices (51, 52) and is configured to convey the signals received from the remote control devices (51, 52) to the electronic control unit, further characterized in that, when the anti-theft device is not in its priority locked state, the electronic control unit is configured in response to receipt of a lock/unlock signal from the first remote control device to actuate the actuator in order to change the position of the locking member from one of its locked or open positions to the other, provided that the vehicle is not in motion or is moving at a rate which is below a predetermined threshold value; and, when the anti-theft device is in its priority locked state, the electronic control unit overrides any signals received from the first remote control device thus negating use of the first remote control device and giving priority to a priority signal received from the second remote control device. a locking member which is mounted adjacent to the drivetrain, downstream of the power plant, and which is movable relative to the drivetrain between an open position, in which the anti-theft device is in its unlocked state, and in which a driveshaft or transmission of the drivetrain is permitted to rotate freely; and an engaged or locked position, in which the locking member prevents displacement of the driveshaft or transmission by locking it in position thus immobilising the vehicle; an actuator which is configured to displace the locking member from one of its open or locked positions to the other; an electronic control unit which is communicatively linked to the actuator in order to control actuation of the actuator, the electronic control unit also being configured to receive a motion signal indicative of movement of the vehicle; and at least one wireless communication module which is communicatively linked to the electronic control unit and is configured wirelessly to receive signals from first and second remote control devices (51, 52) and is configured to convey the signals received from the remote control devices (51, 52) to the electronic control unit, further characterized in that, when the anti-theft device is not in its priority locked state, the electronic control unit is configured in response to receipt of a lock/unlock signal from the first remote control device to actuate the actuator in order to change the position of the locking member from one of its locked or open positions to the other, provided that the vehicle is not in motion or is moving at a rate which is below a predetermined threshold value; and, when the anti-theft device is in its priority locked state, the electronic control unit overrides any signals received from the first remote control device thus negating use of the first remote control device and giving priority to a priority signal received from the second remote control device.