One of the most enduring and memorable relationships in the advertising world has come to an end after the manufacturer of Irn-Bru switched the account to another agency.

After nearly three decades, AG Barr has terminated its long-running partnership with The Leith Agency, based in Edinburgh, and moved its marketing contract to Lucky Generals in London.

Richard Marsham, Leith’s managing partner, confirmed in a social media post that his firm would no longer be working for the Cumbernauld-based company.

Despite being “up for the task” of continuing, he conceded that it “wasn’t to be” and wished the successor agency the best of luck.

Leith produced a string of cheeky and sometimes controversial advertising campaigns ranging from the humorous Sing Song, featuring a family gathered around a piano and the wife declaring that she used to be a man. It was withdrawn following complaints. Perhaps the most enduring was the sentimental parody of The Snowman which became a staple of Christmas TV advertising.

The change of agency follows the arrival of Euan Sutherland who replaced long-serving Roger White as chief executive.

Fans of the old adverts may be encouraged that Lucky Generals have produced some humorous campaigns of their own such as the Yorkshire Tea Where everything’s done proper campaign featuring the Sheffield-born actor Sean Bean.

Mr Marsham said: “What can you say to a 30-year relationship on such an iconic brand! We always said on Bru that we were only as good as the last campaign we’d produced, and being honest, we thought our Euro work for them last year with Mannschaft and others was as clear a demonstration as you could get that we were still more than up for the task.

“But it wasn’t to be and with a new management team at A G Barr comes a desire to try new things. Leith & Irn Bru have produced some of the most memorable and iconic ads over the years that have both entertained and more importantly driven huge commercial value for the company.

“All good things come to an end and this has been a truly remarkable relationship in which clients have become true friends and the legacy of the work will live on.

“We wish A G Barr and Lucky Generals the very best in the next stage of the brand’s history. And as one door closes, hopefully new doors will open. Farewell our crazy ginger amigo and good luck.”

Lucy Henderson, AG Barr’s director of marketing, told the marketing publication The Drum: ““Following an incredibly competitive pitch process, we’ve decided to go in a new direction with the appointment of Lucky Generals, subject to contracts being completed.

“We’re confident that Lucky Generals will deliver creative work that embodies what people know and love about the brand for the next chapter of Irn-Bru.

“We’re immensely grateful to Leith for its talent, dedication and creativity, which has played a major role in the popularity of our campaigns for many years.”