BLM won the business after a shootout against Naked, OMD, Vizeum, Manning Gottlieb Media, Carat, Smarter and incumbent PHD's Rocket.
BLM will work on media planning and buying while Banc has been hired to create the travel and leisure site's next two ads on a project basis.
UK marketing director Vijay Solanki called a review in November last year and said he was looking for more creativity in the company's use of media.
"BLM understood our brand and corporate values. It will offer fresh thinking, strong media planning and consumer insight," Solanki said.
Banc's appointment follows the dotcom parting company with Quiet Storm, which quit the account in December after failing to come to an agreement about switching from project work to a retainer basis.
Banc will create its first work for the online brand in the run-up to Valentine's Day.
If you have an opinion on this or any other issue raised on Brand Republic, join the debate in the Forum here.