Mr Lewis, who angered Labour MPs at the last election by highlighting their past membership of CND, said the unit's main task would be to monitor media interviews and speeches in the Commons by Labour and Liberal Democrat candidates which could be used against them by Conservatives.
"On those occasions when it is necessary to attack bias, I freely acknowledge I will do so, just as the Labour Party feels it is necessary to complain," he said.
He limbered up for the task with a salvo at the BBC over a documentary marking the 50th anniversary of the dropping of the bomb on Hiroshima.
Mr Lewis complained that it was a "biased history programme" featuring an American academic whom he described as one of the "eight founding fellows of the pro-Marxist Institute for Policy Studies" in Washington.
In the past, the Tories' media monitoring unit has been set up only for short periods, in the run-up to a general election or the European elections.
Mr Lewis added yesterday: "It will be salutary for the media to know this unit is back in action."Reuse content