A rotund gentleman will shuffle aimlessly around a polished floor this evening. A sequin-gowned Russian blonde half his age will twirl around him, embellishing his every ponderous move with graceful spins and kicks.

The precise consequences of this event are still hard to predict.

There are some who say that John Sergeant has already made a mockery of the foxtrot. Others say he is merely a product of a political age in which personality trumps policy: that an amiable manner now counts more than a man’s ability to perform a samba.

The most gloomy fear that he will undermine the very foundations of Strictly Come Dancing, so undoing four years of public service broadcasting in which millions have been taught the importance of keeping one’s chest up and head back while waltzing.Such is the influence of Sergeant, 64, the former political journalist whose dancing has lately brought happiness to millions.

Craig Revel Horwood, a West End choreographer and a judge on Strictly, seemed close to despair this week. He told The Times: “This is a dance competition. It’s not Strictly Come Entertainment or Strictly Come John Sergeant. We are supposed to be voting for the best dancer, not the worst.”

Strictly combines an element of oligarchy – four judges whose decision accounts for 50 per cent of the points – with an element of democracy, a telephone vote. Sergeant has consistently produced what the judges have regarded as the worst dance of the evening, but has charmed viewers.

“He really is using every political tool in the book to get votes,” said Revel Horwood. “He is his own spin-doctor.”

Younger voters have mounted a fierce online campaign on his behalf, with Facebook groups called “John Sergeant to win” and “I love John Sergeant and want him to be my granddad”. A middle-market tabloid has run a series of supportive opinion pieces and there has been a bidding war for his dancing memoirs.

Revel Horwood believes that tonight’s contest will be crucial. Whether Sergeant stays in or is knocked out “will decide what this show becomes”, he said. “Is it a ballroom dance competition or is it Saturday Night at the London Palladium, in which case we should just bring in some fire-eaters.”

Mark Foster, the Olympic swimmer who was voted out in the sixth week of the competition, said that Sergeant’s presence had already turned the competition into a pantomime. “It’s frustrating, both for the judges and for the people who are better than him,” he said.

Revel Horwood added: “It puts a lot of pressure on the other dancers. They need to work on their personalities.”

Rival contestants still in the competition are careful not to criticise him. The model Jodie Kidd, rehearsing her quickstep in a dance studio in West London on Thursday, said: “He makes people happy. When the clocks have gone back and its pouring with rain, you want to watch him dance. He’s adorable.”

Did she sometimes wish that she looked more like him? “No,” she said. “That might mean changing my day job.”

Across town, in another studio where sequined dreams are constructed, Tom Chambers, the Holby City actor, was being put through his paces by his partner, Camilla Dallerup. “Ba ba ba ba!” she shouted, stamping her foot. “You need to show that you are in control there. You are leading! Come on!”

Chambers is a favourite to win Strictly, but since last week, when Sergeant remained in and a far more competent dancer was booted off, they are taking nothing for granted.

“Sergeant is the man of the moment,” he said. “I think he has got the whole nation under his, um . . .”

Evil spell? “No, charming spell. He would have made a great Henry V.”

However, he believes that the outcome of Strictly will depend on more than a facility for one-liners. “It’s a bit like running for the White House,” he said. “It’s who you want to stand for the country. It’s the whole package.”

Revel Horwood is not so sure. “It’s about what kind of show people want,” he said. “If they want to see someone wandering aimlessly around the floor, so be it.”

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