Warning: This story contains some minor plot details, which readers may wish to avoid.
Producers of Downton Abbey have been left red-faced after a modern plastic bottle appeared in a promotional photo for the costume drama.
Perched on a mantelpiece behind Hugh Bonneville and Laura Carmichael, the bottle was spotted by eagle-eyed fans when the image was posted on Instagram.
Plastic bottles were not in wide use in the UK until the 1960s - 36 years after the new series of Downton takes place.
The image was later removed from Instagram and the ITV press site.
But one fan offered a potential get-out clause for the makers of the period show.
"Obviously the Crawley family invented the water bottle, and that's how they were able to support the estate," tweeted Diana Pearl.
Downton Abbey employs its own expert, Alastair Bruce, who is in charge of historical accuracy and etiquette.
But this is not the series' first historical blooper, with previous episodes featuring television aerials, double yellow lines and even a modern conservatory.
Viewers have also complained about anachronistic language - including 1960s phrases such as "get stuffed" or "get knotted" - appearing in the script.
But writer Julian Fellowes has strongly defended the show, saying he believes the "the programme is pretty accurate".
"The real problem is with people who are insecure socially, and they think to show how smart they are by picking holes in the programme to promote their own poshness and to show that their knowledge is greater than your knowledge," he said.
The new series of Downton begins in September, and producers have promised the atmosphere in the Abbey will be much lighter than last year.
Series four saw the Crawley family torn apart by the death of Dan Stevens' character, Matthew, while a controversial rape storyline drew hundreds of complaints.
But executive producer Liz Trubridge said viewers "can chortle" again at series five.
"Last series, it was straight after Matthew's death and we couldn't go in with great fun," she said. "We do not have that this year.
"There is, you will be happy to hear, great rivalry again between Mary and Edith."
However, her fellow producer Gareth Neame promised there would still be "right-angle moments you don't expect to happen".
"There is, in all our series, a good mix of high drama and laughs, and there is certainly that mix this time," he added.
The first episode of series five was shown to the press on Thursday, and contained the usual mix of secrets. schemes, seduction and skullduggery.
Set in 1924, the programme reflects the election of the UK's first Labour government - causing consternation for the Crawleys, who assume that a socialist ruling party will start to dismantle their estate.
"Those upstairs see it as a direct threat to their way of life," said Neame. "The characters below stairs see it as an opportunity for huge change."
The first episode also sees a dramatic night-time fire in the Abbey, with several secrets revealed as the occupants flee for safety.
Trubridge said the production team had been required to build a replica set for the sequence in Ealing Studios, as it was too risky to film the blaze at Highclere Castle - the Hampshire estate where the programme is usually filmed.
"Because it was a stately home we couldn't set fire to it - the owners didn't want smoke damage to their house."
The new series also sees plenty of will-they-won't-they relationships - with Lady Mary (Michelle Dockery), Isobel Crawley (Penelope Wilton) and Tom Branson (Allen Leach) all receiving advances from potential partners.
Meanwhile, lady's maid Anna Bates (Joanne Froggatt) is still struggling to come to terms with her rape, and the mysterious death of the man who attacked her.
The harrowing attack prompted more than 200 complaints to media watchdog Ofcom last year but the show, which was broadcast after the 9pm watershed, was cleared of breaching broadcasting regulations.
Froggatt said she had not received any personal criticism from the public.
"It's all been positive in responses to the storyline," she said. "I got a small number of letters from women who'd gone through similar experiences and felt Anna was a character they could connect with.
"That was very touching for me. It was a moving experience."
In the new series, her character still finds it hard to contemplate a physical relationship with her husband John (Brendan Coyle), and closes down any suggestion of starting a family.
Meanwhile, some of the servants suspect John is responsible for the death of her attacker - but Froggatt insisted her character was not one of them.
"I don't think Anna thinks for a moment that Bates is a serial killer," she said. "What I'd like to see for Anna and Bates as a viewer is different from what I'd like as an actor, because you like to play the drama, but it's important to have the happy times in between.
"They get moments of happiness and positivity for them, but it's not an easy journey."