Sitting on their sofas this summer, television viewers glimpsed a brighter world full of better-looking people and bigger sofas.

The people jumped around in front of their large sofas and mimed the lyrics of a rock song that speaks to anyone who aspires to live with enormous household furniture: “I want . . . a bathroom I can play baseball in and a king-sized tub big enough for ten plus me.”

If viewers thought these joyful scenes, part of an advert for the department store DFS, were too good to be true, then they were right. The sofas were too big.

The Advertising Standards Authority has now rebuked the furniture retailer for displaying technically enhanced sofas. The actors in the commercial had in fact been dancing in front of a green screen on to which DFS had later superimposed footage of sofas.

The authority upheld complaints from 21 members of the public, that these superimposed sofas appeared larger than the real thing.

DFS said that it had shot the actors in front of the screen so that it could vary the sofas on display in adverts.

It said a real sofa had been used as a “point of reference”, and that it had taken “particular care to ensure that the new superimposed sofas appeared as real in their chosen background as possible”.

The real people watching on their real sofas were not impressed. Figures from the polling agency YouGov’s BrandIndex show that in the week after the advert was first aired, respect for the brand DFS plummeted.

Campaign magazine, the bible of the advertising industry, named the advert as its “turkey of the week”, saying that it had “all the subtlety of a smack on the head with a sofa”.

Christopher Graham, the director general of the authority, said the advert flouted a very basic principle — that “you’ve got to be able to prove the claim that you’ve made”.

“In this example, the whole thing talks about aspiring to have a ‘king-size tub big enough for ten’, and about a ‘huge range’. The impression that is being given is that you get a hell of a lot for your money and the problem is that the advertiser wasn’t able to substantiate this claim.

“You can’t say you can buy something the size of a stretch limo if, when you get to the showroom, the reality is a bit more prosaic.”

DFS insisted that it “never had any intention to distort the perspective of its products”. It argued that to do so would have been counterproductive, as customers only bought sofas having visited a store and seen the product.

“The main concern of many customers when buying a new sofa is that it may be too large to fit into their house or flat, so exaggerating the size of products would actually have been a deterrent rather than an aid to sales,” it said.

The advert was intended to allude to the video of a single by the Canadian rock band Nickelback, which showed actors lip-synching lyrics such as: “I need a credit card that’s got no limit, and a big black jet with a bedroom in it, I wanna be a rockstar.”

The advert concluded: “You don’t need to be a rock star to afford a new sofa in the DFS sale.”

If the advert has damaged the brand of DFS, it has also had a strange effect on the image of the anarchic rock band that wrote the song. Playing at Wembley Arena in September, Chad Kroeger, Nickelback’s frontman, who is also rather larger than life, suffered the indignity of hearing his fans chant “DFS” before he played the single.

“You know you’ve made it when your song makes it into a sofa commercial,” he observed. “That’s when you know you’re at the pinnacle of your career.”

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