Welcome to the forum Tom, the helmet appears to be British made not Belgium they produced their
Brodie helmets post WW2. The stamp mark L33 is the Batch number of Steel used and dated 1941,
The BMB liner is missing it's rubber X shape piece which may have been broken off leaving the round
piece of rough looking rubber behind. Not all manufacturers stamped their names on the rim, the screw
holding the liner in place is not original.
Hope this helps.