Christmas '75 - Learning to Drive (special episode). When Frank is driving the white mini in the country lane, trying to overtake the lady on the bike, there is nothing behind the mini, but then a split second later he is being followed by a silver Renault. As he tries to overtake the cyclist, Frank is followed by a brown Triumph, then a second later a yellow Ford Anglia is following him. Frank also appears to drive along the same stretch of road several times, as he keeps passing the same parked cars.
Australia House (Series 3). When the phone rings asking Frank to go and have a look at the electrics in a house, the address he is given over the phone to him which is written down by Betty is "26 Upton down". However when Frank arrives the number on the door is 24.
Christmas '75 - Learning to Drive (special episode). When Frank is taking his driving test in the Hillman Imp, he is driving slowly down a narrow and winding road. He is being followed by the green van, flashing its lights at him, and as the van turns off Frank hears a train hoot, then drives round the barriers at a level crossing. The terrain suddenly changes from a narrow road in the hills, to a wide road on flat land. Then while Frank is driving to the sea, he passes the same parked brown Vauxhall Victor twice.
Cliffhanger (Series 2). When Frank is climbing over the front of the car to get to the boot a rope is visible through the rear window that is clearly holding the car or holding Frank in some way.