The year was revealed to be 1988 on the bottom of a drink can discarded by the girl driving the car, but when the camera returns to the inside of the car, the sound system was a modern late 2000's CD player.
When Jonathan and Joey are trapped in the cellar Jonathan mention Francis Galton and says he became friendly with Charles Darwin - Francis Galton was Darwin's half cousin, Jonathan would have known that.
When Hugo Dore picks up his copy of 'The Daughter of the Sphynx' from the bookshelf, he is holding a white cup in his right hand. When the camera angle changes, his is no longer holding the cup and has had no opportunity to put it down.
During the vicars introductory scene in this episode, the long haired cat which that triggers his allergy is supposed to settle by the bird table. He is indeed seen to jump onto an adjacent picnic table. However, from the angle of his landing (coming down, rather than jumping up) it is obvious he was thrown by some off-screen crew member rather than coaxed up on cue of his own accord.