When Hacker's driver is driving him, he never turns the steering wheel of the car, revealing it to be a set.
Jim Hacker's desk in his office has drawers both on the side on which he sits and the other side also. It is clearly a partner's desk, designed to be used by two people facing each other. However, as the government minister, there is no reason why Jim would have such a desk. Neither Sir Humphrey nor Bernard work at the same desk or even in the same office as Jim Hacker.
Jim Hacker's driver is normally called George and is listed as such in the credits. However, for some reason in this episode he is referred to as "Roy".