Old Thriller Film..........?

There are a couple living in a old Mansion which has a portrait of the same mansion and drive on the living room wall...

They notice a dark ghostly figure in a long black monks habit has appeared in the Painting.. and it starts moving nearer to the front door, at the end of the film, they look at the painting, and the 'figure' is on the doorstep, and they hear knocking at thier own real front door....

it was shown (i think) on Ch4 England in the early eighties.