Clemmow Hornby Inge has resigned the £13.7 million Expedia advertising account, citing creative differences.
Expedia was CHI's biggest-spending client in 2004 and is the UK's leading online travel agent. It will now hunt for a successor agency.
The agency/client relationship has been strained for some time, according to sources. Beverly Shaw, the marketing director who appointed CHI two years ago, left in 2003 and was replaced by Elyas Chowdhury. He had been promoted from marketing manager.
CHI terminated the relationship last week, but has committed to continue working on the account until Expedia finds a replacement.
In a joint statement, the CHI managing partner, Johnny Hornby, and the managing director of Expedia.co.uk, Dermot Halpin, said it was in both parties' interests that they terminated their business relationship.
"We have enjoyed a mutually rewarding business relationship that has seen us work together to deliver some effective campaigns, but we've both agreed that the future creative direction for the businesses was probably best pursued separately."
However, evidence of a deeper rift has come to light, following a subsequent statement from Chowdhury.
"Expedia and CHI agreed this split amicably, and I am very disappointed with the one-sided way it has been presented to the press. As always, it's never the whole story, but we're not interested in descending into a slanging match. Our preference is to move on professionally and find the right agency for our business and brand," Chowdhury said.
Hornby responded: "It's a shame because 'create your perfect trip' demonstrates our big-ideas thinking at its best. I hope it forms a strong foundation for Expedia to grow in the future."
CHI introduced its "create your perfect trip" advertising, in April 2003.
The brand's adspend rose from £4 million to £12 million over 18 months.
The campaign, which emphasised the company's ability to offer customers their entire travel itinerary, ran across TV, press and outdoor.
The activity aimed to change perceptions that the internet was best used for booking cheap flights,and instead encourage consumers to book their whole holidays online.
Since the campaign broke, Expedia has overtaken Lastminute.com as the UK's leading online travel agent.
The blow of parting with Expedia will have been cushioned by CHI's capture of the £40 million Direct Line advertising account in December.