The Builders - S1-E2
Revealing mistake: Look at the skirting board of the section of wall Basil hits Manuel against. There are black shoe marks on the paint from previous takes where Manuel kicks the board. (00:16:15)
Revealing mistake: When Manuel throws the grapefruit at the other guests, you can see the woman closest to the camera react before Manuel throws it. (00:11:00)
Revealing mistake: When Basil sends the grapefruit flying, we see Polly go through the doors to the kitchen. However, if you look closely at the doors as she goes through you will see just a plain wall. Not the kitchen as is seen in other episodes. (00:11:00)
The Builders - S1-E2
Other mistake: In the end credits, Major Gowen's surname is incorrectly spelled "Gowan."
The Builders - S1-E2
Visible crew/equipment: When the Major says "He lost it you know" to Polly before entering the dining room, the silhouette of a boom mic can be seen on the top right hand of shot. (00:25:20)
The Wedding Party (a.k.a. Sex) - S1-E3
Revealing mistake: Basil goes back to the second floor chasing after Polly. As he passes the last part of the banister, he touches the edge of it and it wobbles like rubber. (00:24:00)
The Germans - S1-E6
Character mistake: When the first German guest enters reception, he asks Polly, in German, if she would tell him what time lunch is served. She replies in German "at 9am, in five minutes." Which would be a strange time to be serving lunch! Actually her pronunciation of "9" sounds more like the German word for "no", so could be mistaken for "at no time. In 5 minutes."
Suggested correction: He asks what time lunch is being served. Lunch would not be served at 9am, it would be served around midday. Polly's response is "In no time. In 5 minutes" is absolutely correct. She does say "nein", not "neun" but it is not a mistake.
Visible crew/equipment: When Basil enters the "Private" room, the camera is reflected on the glass door pane.
Suggested correction: This is way too vague to be accurate. The office (which has private on both doors) is visited by Basil on innumerable occasions throughout this episode and so needs to be more precise.