no it can't be either of them - they would be the first people you suspect.

Maybe it was the well known female impersonator Hercule Poirot, dressed up as miss Marple's dim housemaid, entered the doctor's surgery when no one was looking, with an authentic common working class accent said, "Fancy a cup of char dearie...?", switched the bodies round, and everybody thought it was the village solicitor when in fact was the ingenue starring that week at Sidmouth Little Theatre in a production of No Calcutta!(Similar to Oh Calcutta! but the cast wear woolly combinations out of respect for Sidmouth and the fallen of two wars).

seems a more likely explanation to me.......