Downton Abbey: 2014 Christmas Special, ITV

“But I do want to be stuck with you.” Five series and five Christmas specials down, Downton fans heard a line of dialogue they had no idea they’d been waiting for all this time. Never mind that the scenario was a straight lift from The Remains of the Day, in which the stuffy old butler proposes to the starchy old housekeeper. Stone the crows and knock us all down with a feather, Carson popped the question to Mrs Hughes.

And what, of all the wonderfully blindsiding things, did she say in reply? “I thought you’d never ask.” Jim Carter and Phyllis Logan, the show’s gnarliest pair of troopers, rose splendidly to the occasion. 

After a full tariff of births, deaths and marriages, it turns out that Downton Abbey still has the ability to move and surprise. The other scene which set the pulse racing was of a different order. Lord Sinderby’s mistress and illegitimate child turned up unexpectedly in the midst of a party, the innocent agents of a trick played by scheming Thomas upon Alun Armstrong's toxically snobbish butler. The resourceful Lady Rose (Lily James) swept in to save her father-in-law from exposure and humiliation.

It's been fun having Rose as Sybil's replacement, but it seems that this may be her swansong. Without wishing to sound like The Times's court circular, her new husband Atticus has a job offer in New York. Indeed, with Branson (as Maggie Smith’s Dowager Countess still refers to her grandson-in-law) off to Boston, can Downton Abbey US be far down the pipeline? Lady Cora's mother, in the person of Shirley Macleine, awaits to make up the numbers. Certainly the UK edition is starting to cough and shuffle its feet and tie up loose ends as if its work here is done.

The Bateses’ calamitous flirtation with the law can surely be allowed to continue no longer. Lady Edith’s last obstacle to outing herself as Marigold’s mother is breaking the news to her older sister. She may even have a new man to play opposite, while Lady Mary has sourced a car fanatic (played by Matthew Goode, pictured below with Michelle Dockery), presumably with an eventual view to matrimony. You hope he's a better driver than the last incumbent. The minor matter of Cousin Isabel’s on-off engagement needs resolving, and Daisy's future as a bluestocking farmer to be determined. If only a nice young man could be found for Thomas the footman, one’s cup of joy would overflow.

This was a long, episodic and ambitiously convoluted show, set partly around the Glorious Twelfth (August to the non-grouse shooters among us) and latterly at Christmas. Another turn around the mulberry bush has been announced for the coming autumn, but there is strong evidence that Julian Fellowes may finally be running out of options. Having scripted his way from 1911 to 1924, he's now reached a place where knowing nods and winks are irresistible, and the odd tired sigh inevitable. Thomas’s resourcefuness is now a family joke, it seems. “Can’t Barrow come up with something?” said Lady Mary when Lord Sinderby’s butler needed bringing down a peg or two. Then came the dull running spat between Spratt (Jeremy Swift) and Denker (Sue Johnston), happily nixed by the Dowager Countess. “There is a point,” she advised, “where malice ceases to be amusing.” When Cousin Violet is no longer up for a laugh, the game is surely moving into injury time.

The toes curled most of all when, for convenience, characters produced back stories like rabbits out of a hat: first Mrs Hughes’s dependent sister, then Anna’s molesting stepfather. Who knew? Certainly not the actors before they received the script, and probably not Fellowes either until he needed to cook up some fresh motives to get him out of a hole.

Humbugging aside, there was quite a bit of fun to be had here and there. Hugh Bonneville’s Lord Grantham, off the sauce owing to an ulcer, got wonderfully sozzled at the Christmas Eve carols. Jane Lapotaire was blessedly sour as the long-lost Princess Kuragin, whom one could imagine ripping her love rival from the coach in which her husband was eloping in St Petersburg half a century before. Perhaps, in addition to the US Downton franchise, we could have the Russian prequel. Downton goes East and West? There's a bit of gas in the old jalopy after all. Just not as we know it.