Reporters and producers working at Westminster and on sensitive programmes such as Radio 4's Today are being told to report attempts to bring "undue pressure" to bear.
The unit was set up in secret two weeks ago. Every Tuesday the senior manager who runs it supplies a report to Tony Hall, director of news and current affairs at the BBC. "We are not taping calls," Mr Hall told the Independent on Sunday. "Not yet."
First evidence of the corporation's readiness to impose sanctions on unacceptable political pressure came two days ago when John Birt, director- general of the BBC, publicly rebuked Alastair Campbell, press secretary to Tony Blair, for his "crass and inappropriate" fax requesting top TV news billing for the Labour leader's party conference speech rather than the verdict in the OJ Simpson trial.
Yesterday, Labour returned to the fray with a vigorous defence of the Brighton fax, and accused the Tories of putting Mr Birt under pressure practically every day of the week. Mr Frank Dobson, the shadow environment secretary, said on the Today programme: "I have never heard him describe that as crass."
He added: "I would like to make a positive suggestion. Will John Birt log all the representations he receives from all political parties, and publish them monthy?"
Unbeknown to Mr Dobson, the BBC had already implemented his proposal, though it has no plans to publish the log. Mr Hall said: "Two weeks ago, I set up a system for looking at all the calls, either complaints or those seeking to influence the running order or content of whatever we are doing politically. I review that log once a week with senior managers and we decide what action, if any, we take."
The BBC distinguished between calls that properly sought to put across a point of view and those that were, on occasion, "frankly abusive", he added. "There has been a lot of pressure over the last two weeks from all parties, particularly over the last week from Labour.
"There has always been pressure at conference time and in the run-up to the general election. That is a fact of life. This time there are more of them, and they seek to influence what we are doing more of the time. It is intimidatory, and sometimes abusive."
Mr Hall gave examples. "It is seeking to know where items are in the running order, to know what is being headlined and what is not; where a story is developing, and if it is developing or not.
"We have seen a step-change in the amount of pressure and the volume and frequency of pressure being put on programmers. We want to make sure we distinguish between improper and proper pressure. There is nothing wrong with politicians seeking to influence or give information to journalists. But it gets wrong when it's over-pushy. There is too much of it and it is deliberately manipulative."
The BBC's move to head off "intimidation" will be received at Westminster with a mixture of alarm and bravado. Spin doctors of both parties, but particularly Labour, have increasingly taken for granted their right to browbeat political reporters into following their agenda.
The row over manipulation tomorrow moves to Blackpool, where Labour is to stage an unprecedented monitoring operation on the Conservative Party conference. Frank Dobson and other Shadow Cabinet colleagues will be in charge of a six-strong "response and rebuttal" unit.
"Every lie they tell about Labour we will rebut," said a senior Labour Party aide. "Every division of theirs, every inadequacy we will expose. It is part of the Blair view that you never rest or sleep."
Taming the conference, page 10; Alan Watkins, page 20; Neal Ascherson, leading article, page 21