The new "Mmmutual" message is reinforced in a spot which features a giant Victoria sponge-cake.
The ad is the first to be produced for Britannia by McCann-Erickson Manchester since it took over its £4 million creative account from Walsh Trott Chick Smith at the beginning of the year.
Manning Gottlieb OMD is planning and buying media for the campaign which will break on 19 March and will run until August across the ITV network, on Channel 4, five and satellite stations.
The ad, produced by the agency's creative partners, Dave Price and Neil Lancaster, demonstrates the benefits of mutuality by showing a Britannia advisor and a customer sharing the cake.
Alan Long, the Britannia's head of marketing, said: "This campaign really focuses on what's different about a mutual society and what makes Britannia Britain's best mutual. It's an exciting time for us and we think this will help us to clearly stand out from the competition."
The "Mmmutual" theme will also run across supporting press and online advertising.
Peter Gamble, the McCann Manchester managing partner, said: "This idea allows us to integrate our communications strategy at every level."