Proximity, which is affiliated with Omnicom's Abbott Mead Vickers BBDO, won the pitch in a review which was handled by the Haystack Group, after a final shoot-out against Arc.
Although not a joint pitch, Proximity and Arc partnered with their above-the-line sister agencies AMV and Leo Burnett respectively to demonstrate to Britannia Music that they had the necessary experience in TV advertising.
Britannia Music has appointed Proximity ahead of a total brand overhaul, which will see a new identity being created by Wolff Olins.
Proximity will be given the task of developing brand response campaigns using press, posters, direct marketing and online activity.
It is understood that if Britannia Music does decide to expand its advertising remit to include television work, then a further pitch could be undertaken.
In such a case, AMV would be in the running to pick up the work.
Previously, Britannia Music used a range of marketing agencies and has not had a lead agency.
It is understood that the planning and buying account has gone to MediaCom, but Britannia Music's marketing director, Adam Tuson, would not confirm the speculation. The account was previously shared by Carat and MediaVest Manchester.
Britannia Music's managing director, Ford Ennals, who was appointed in July, made the final decision.