Banc has unveiled its first work for the Liberal Democrats in the run-up to this year's election.
The poster features the party's leader, Charles Kennedy, and the strapline: 'I jump on injustice, not bandwagons.'
The one-off execution will be followed by further above-the-line work, focusing on the party's claim that it will fight its election campaign based on real, 'principled' issues on which Labour has failed to deliver and the Conservatives are divided.
Further work will be rolled out once the Government has declared its campaign. The party is thought to be spending pounds 3 million through Banc.
Banc's chairman, Robert Bean, said: 'The Liberal Democrats realise that a school-boy scrap is not advancing the cause of democracy. Charles and the party are taking a leadership stance, setting a more relevant agenda.'
He said the agency was attracted by the party's cause because of its value-driven, rather than dogma-driven, attitude towards the election.
Kennedy said in a statement: 'The Liberal Democrats will address the great injustices in Britain today during our campaign.
'We will stand up for social and individual injustice. We will continue to oppose illiberal government measures.'
The work was created by Banc's director of advertising, Peter Harold, and the photographer was Tim O'Sullivan. Media planning and buying is by GJR.
Banc won the account to handle all aspects of the party's communication strategy in January. The appointment, made without a competitive pitch, marked a reversal of its 1997 decision to handle its advertising in-house.
The Liberal Democrats' director of communications, David Walter, said that the campaign was designed not to underestimate the electorate, and had a greater creative clout than the work produced in-house.
The 1997 campaign depicted a poster of Tony Blair as Punch and John Major as Judy. The party decided to go it alone after the liquidation of the incumbent agency Knight Leach Delaney.