The final episode of the BBC series kicked off in Billericay and Barry, but the cast were soon speeding down to the south coast to prevent Nessa, played by Ruth Jones, from leaving the docks to work on a cargo ship in Curacao.
But while ABP signs sporting ‘Port of Southampton’ were in shot, locals quickly noticed that none of the Southampton scenes were actually shot in the city.
The scenes were instead filmed at Newport Docks in Wales, 100 miles away.
“Being someone who has worked in Southampton docks, I can tell you it wasn’t Southampton docks,” Lane Coombs said on Facebook.
Katie Williamson agreed, saying that it looked like stock footage and was way too hilly in the background when Ruth Jones’ character was stood on a boat.
“Hills in the background sounds like a rookie mistake,” Phil Jury said in agreement.
“Should’ve filmed it in Southampton if that’s what they were going for.”
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There was one shot that featured the real ABP Dock Gate Eight entrance as Nessa ‘arrived’ in the city by coach.
But this was simply the top part of the entrance, which is visible next to the Holiday Inn on Mayflower Roundabout, superimposed onto the entrance of Newport Docks.
Residents also laughed as it looked like the Titanic was visible through the bridge.
Tim Carey said it was ‘Southampton in name only’ with artificial signs plastered everywhere.
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The main cast of characters were stuck on a coach while they raced to Southampton to stop Nessa from boarding the ship and leaving.
But they were gridlocked in a country lane, and Steven Galton joked that if they were going to be stuck in traffic, it would surely be on the M27.
Other than the Southampton gaffe, which would not be recognised by anyone who is not local to the city, the Gavin and Stacey finale was very well-received.
It secured the highest overnight Christmas Day ratings since 2008 after drawing in an average 12.3 million viewers.
The emotional farewell to the beloved show surpassed the amount of viewers that the 2019 Christmas special racked up by more than half a million.
You can now watch the highly-anticipated season finale on BBC iPlayer.