More than 30 years ago, Carlsberg established the "probably the best lager in the world" campaign.
In recent times, Saatchi & Saatchi has produced some of its best work, including 2006's "Old Lions" and the recently released "Carlsberg wives" for the brand by extending the premise to "Carlsberg don't do X, but if they did it would probably be the best X in the world".
Advertising's history is full of successful long-running campaigns. However, there are hundreds more that overstayed their welcome and were kicked to the kerb.
Kate Stanners, the executive creative director at Saatchi & Saatchi, says one advantage of long-running campaigns is that they breed constant creativity if you have a receptive client. "The creatives are constantly coming up with their own ads because you don't need a specific brief. The idea is already there," she says.
A long-running campaign can move the brand so far into the nation's psyche that it becomes part of the vernacular, and these days it also means it becomes part of our daily communication via consumer-created content.
Nikki Crumpton, the executive planning director at McCann Erickson, says: "Cultural developments are extremely important. People's attitudes change. If the campaign or idea starts to be less effective at plugging the brand into the culture that surrounds it, then it's a good time to rethink it."
Darran Britton, the marketing director at Carlsberg UK, adds: "It is often said in marketing that 'familiarity breeds favourability' but we have found that familiarity breeds adoption by the consumer."
Because of these points, and the time and money invested in forcing them into the nation's awareness, agencies often fight hard to keep a campaign before killing it off.
Richard Warren, the communication strategy director at Delaney Lund Knox Warren & Partners, the creator of the irritatingly recognisable singing Howard who fronts the Halifax ads, warns that vigilance is of the essence if you don't want your hand to be forced into killing a campaign.
"The financial services sector is extremely low interest and all about salience. Howard is so recognisable he has a massive impact on the salient consumer. However, in 2005 we realised, through observing the irritation metric, people were getting pissed off - he just had too much coverage, so we started putting other people in the ad to keep the campaign going."
But Crumpton argues that some campaigns are not worth fighting for: "There are long- running campaigns that should have been strangled at inception let alone been given a second, third or more chance of polluting the airways."
Jonathan Burley, the executive creative director at Leo Burnett and Arc, believes it is laziness that leads to this. "The idea can become familiar, the execution needs to be refreshed so you don't get forced into a structure," he says.
Stanners also believes that if a client doesn't understand the process they can call time on a campaign out of panic. "All they have is intellectual property, but the idea isn't really theirs any more, it belongs to the populace. In the past it was a controlled piece of advertising, but not any more."
The overall consensus seems to be that as long as the idea is refreshed and the work is developed to match consumer culture, then it is worth fighting to save.
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PLANNER - Richard Warren, communication strategy director, Delaney Lund Knox Warren & Partners
"A campaign will die in one of two ways. Either the metrics will deteriorate or the people will just get fed up with it.
"When dealing with a long-running campaign, you need to constantly analyse the irritation metric and analyse the tracking.
"Advertising is a small thing in people's lives, so too much of it is way too irritating for a lot of people. However, there are always ways to keep it going. You just have to keep learning from your mistakes. It's worth it if the campaign is still effective and creative."
PLANNER - Nikki Crumpton, executive planning director, McCann Erickson
"My feeling is we shouldn't be aspiring to long-running campaigns, but to long-running ideas. As to the shelf life of an idea, we have come full circle.
"At the end of the day, a campaign should only ever run and be allowed to continue running if it is able to deliver significant returns on investment, from both a financial and an emotional perspective. And if it's able to do that let it run.
"However, if it feels difficult it's probably either run out of steam as an idea or, as is more often the case, the execution has overshadowed the idea and that straight-jacket needs to be taken off and shoved in the bin."
CLIENT - Darran Britton, marketing director, Carlsberg UK
"In essence, the campaign is based on an unchanging truth about the brand and in that context Carlsberg has not seen the need to 'change' the core thought. Each execution represents an incremental investment in the brand.
"We found that our continued investment in the 'Probably the best' line had paid off; consumers remembered it, associated it with the brand, believed us and, in recent times, interacted with it.
"From the start of the campaign when people started sending e-mails with 'Carlsberg don't do housemates' around the first series of Big Brother, right up to today where consumers regularly post their own 'Carlsberg don't do' ads on YouTube."
CREATIVE - Jonathan Burley, executive creative director, Leo Burnett and Arc
"It sounds obvious but you have to get it right. The best long-running campaigns are based on tonal ideas, and not executional. Honda and Tango both got this right. With these two you never knew what was coming next. If you follow the second route, ads can quickly become lazy. Also, if you kill a campaign, you'd better make sure you have something good coming. When I was at WCRS, they got rid of 'I bet he drinks Carling Black Label' and the advertising has suffered since. It's only now getting slightly better."