The move follows the resignation of the account by the incumbent, Karmarama, over creative differences.
It is understood that Karmarama resigned the account owing to differences with the client over the implementation of the creative idea at the heart of the brand's launch campaign.
Karmarama's first and only work for Sen is due to break imminently to support the opening of the chain's first store on London's South Molton Street. The campaign will run until Christmas.
Sen, which has yet to start talks with other creative agencies, is to begin the hunt for a replacement shop in the New Year. Its first major heavyweight campaign is earmarked to launch next April.
The national and global roll-out of the chain is backed by a media strategy devised by the communications strategist Naked.
The brand Sen was created by Wolff Olins and its for-mer creative director, Doug Hamilton, who now works for Hutchison Whampoa.
Hutchison Whampoa is aiming to tap into the growing popularity of "wellbeing" products and therapies and will be positioned against chains such as Boots and Holland & Barrett.
The stores will also promote Chinese culture and offer personal consultation by qualified practitioners.
Hutchison Whampoa also owns the Superdrug chain and is gearing up to launch 3, the third-generation mobile network to compete against the likes of Orange, O2, T-Mobile and Vodafone.