Revealing mistake: When Maggie vomits into her cup it is obvious that it is spilling from her chin rather than her mouth.
Revealing mistake: When Lou and Andy are in the pub we see a closeup of a person's hands on a slot machine. It is obviously in Demo mode because every button is flashing. This does not happen when you are playing for real.
Revealing mistake: When Bubbles rips her wig off, her face is obviously paler than the top of her head, due to the fat-suit Matt Lucas was wearing.
Revealing mistake: Just before Andy pushes Francesca down the stairs in her wheelchair, we see Lou walking down the steps, and they are quite steep. However, when Francesca goes down the stairs in her wheelchair she doesn't have much of a bumpy ride, despite the steps. A ramp was put there - you may need to look very carefully and you see it pop up slightly from the steps. [A reasonable way to prevent injury but it is still a mistake.]
Answer: She played an elderly (and presumably gay) resident of Llandewi Breffi, Daffyd's village.
Sierra1 ★