Lock mechanism with blocking member

A locking mechanism comprises a drive bar 18 which co-operates with latches at remote locations on a door and a blocking member 14 which passes through an aperture 20 in the drive bar 18 in order to prevent or restrict movement of the drive bar 18. The blocking member 14 may also engage a safety lever 4 to limit the extent to which the door may be opened, controlled by the length of the lever 4. The blocking member 14 may be generally box shaped 14b with a cylindrical head 14a. The lock may be operated by a remote control device powered by a battery or a solar panel. The locking mechanism may further comprise a hooked shaped locking member which engages the door frame to provide additional security (figure 6).