In his speech, The Trouble with Trust, the BBC director-general Mark Thompson called for greater transparency in the BBC's dealings with political parties:

"There are steps we should take to make our own dealings with politicians and other public figures more open to scrutiny. When A refuses to debate with B or sets other conditions before an interview or debate, there's often a case for letting the public know - for example, via the Editors' Blog..."

So here goes. This week, for the first time in my three years as executive editor of Question Time, we were told by Downing Street that a cabinet minister would only appear on the programme if another member of the panel was replaced. According to No 10, a senior member of the cabinet was available to do Question Time but only if Alastair Campbell was replaced by a member of the shadow cabinet.

Very obviously, we refused and as a result no minister appeared, meaning that the government was not represented on the country's most-watched political programme in Queen's Speech week - one of the most important moments in the Parliamentary calendar.

No 10 stated that the objection to Alastair Campbell was that he was not an elected Labour representative or a front-bencher. Not only is Alastair Campbell one of the most senior and influential figures in the Labour movement - an architect of New Labour - but Labour ministers regularly appeared on Question Time panels when the then opposition was represented either by someone outside of the front bench or by an unelected panellist - sometimes even a prospective Parliamentary candidate. It is not an argument or an objection that bears scrutiny.

It is a fundamental principle of our independence that politicians cannot dictate who sits on the panel. It is for Question Time, not for political parties, to make judgements about impartiality and to determine who is invited to appear in the interests of the audience. Parties are free of course to accept or reject those invitations, but they do not have a right of veto over other panellists. Licence fee payers rightly insist that the BBC must be free from political interference.

Gavin Allen is executive editor, Question Time.