Continuity mistake: On the episode where Smithy goes AWOL learning he's to be a father, Nessa goes home to Pam's house along with Stacey and Gwen, and in that scene you can see the tattoo on her arm of the Welsh dragon. If you focus enough you can see the dragon only has 3 legs, whereas the Welsh dragon has 4 legs. This isn't a factual error as her tattoo usually has 4 legs. Both writer Ruth Jones and director Christine Gernon confirmed this on an outtakes special.
Continuity mistake: On Gavin and Stacey's wedding episode in the reception, Dawn is talking to Pam and Gwen about the fact that she and Pete's sex-life is dead. Then, Smithy taps on a glass to indicate the speeches beginning, but as the glass is being tapped Smithy is in the shot with his blazer on, talking to Bryn. Then the shot pans over to the other end of the table, and Smithy is suddenly stood up with his blazer off.