Requests for ministers to appear on Today could be denied by the party if John Humphrys persists in interrupting them and denying them the opportunity to put their views to the listeners, David Hill, director of communications, said in an exchange of correspondence leaked to the Liberal Democrats.
After an interview with Harriet Harman, Secretary of State for Social Security, on lone parents' benefit on Wednesday, Mr Hill wrote to John Barton, the editor: "We ... are seriously considering whether, as a party, we will suspend co-operation when you make bids through us for government ministers."
Although programmes make interview requests directly to departments, party headquarters acts as a clearing house and because of tight links between party and government, Mr Hill probably speaks for all ministers. He told Mr Barton the whole of Millbank headquarters was talking about the interview "when I got back from the 9am meeting" - the daily media co-ordination meeting chaired by Peter Mandelson, Minister without Portfolio, and attended by Alastair Campbell, the Prime Minister's Chief Press Secretary.
Mr Hill said that after the "ridiculous exchange" and the repeated interruptions no one would have been any the wiser as to Ms Harman's explanation of government policy - a point made by some Labour backbench critics after she wound up the Commons debate that night. Mr Barton said he was surprised: Ms Harman had not complained at the time and had answered questions at length. "I felt this morning that I was listening to a rigorous, fair- minded interview which illuminated an important policy issue."
Mr Barton said listeners would be the losers from any suspension of co- operation and that he was completely satisfied they would continue to have a good working relationship with Labour. "We have received full co-operation since the exchange of letters. The matter is now at an end."
A BBC spokesman said: "We take everything the political parties say to us seriously, but we are an independent public-service broadcaster and the remit for our interviewers is to ask the questions that we believe the public, our listeners, want answered."
They certainly did not perceive there to be a "John Humphrys problem. He is one of our top political interviewers. We believe he got it right." A source said a Humphrys interview with Gordon Brown, the Chancellor, the following morning had, if anything, been more robust than the one with Ms Harman.