Thank you very much Thomas! It appears my lever is just bent a little as Daniel suggested and my "catch" is complete 
My pleasure, Nick!
Mine, btw, only works when I have this lump of tinfoil wedged under the hammer-head and "anvil", so that the hammer stays lifted up a little... The tinplate nose inside the contraption that lifts the hammer has obviously been bent and straightened and bent again and again so that it does work only haphazardly (and I don't want to dismantle the whole body as the parts a held together by rather frail tinplate flaps...).
But I like the way it works and the way it looks!