Episode One - S1-E1
Revealing mistake: When Gavin and Stacey meet, look at the people all around them in Leicester Square - many of them are stood watching the filming.
Episode Two - S2-E2
Revealing mistake: When Pam opens the door to Gavin Mick Bryn and smithy after smithy went to the driving range you can see 2 Welsh dragons on the mural behind Pam. Even though Pam and Mick's house is filmed in Wales they live in Essex in the show, in England.
Episode Six - S1-E6
Other mistake: After the wedding when everyone is outside, Smithy says he has forgotten the maps that gave directions to the reception. Bryan says he can use the sat nav in his Picasso and tells everyone to follow him. But he was driven to the church in the Bentley with Stacey, so his car wouldn't have been there.
Trivia: The three main families in the show are named after British serial killers (West, Sutcliffe and Shipman).