Miss Grant goes to the door

I have read briefly about this film somewhere, it's supposed to be a "thriller" thats aimed at teaching people how to stay sharp and on the lookout during the war,

Seems all really tongue in cheek by todays standards, two maids being tricked into information by a german pretending to be a british soldier, but they catch him out.

I wondered if anyone knew where I might be able to get a copy of this film to watch.

Thanks