Senior MPs have questioned the position of the Iraq inquiry’s top official after it emerged that she gave US diplomats information from inside the inquiry while still working in her permanent role as a government foreign policy adviser.

According to a US embassy cable disclosed by Wikileaks, inquiry secretary Margaret Aldred briefed an embassy official about the inquiry’s secret plans to visit Washington for “private” discussions about Iraq.

The new revelation places Aldred at the heart of a plan to protect US interests during the inquiry. It adds to concerns about the process by which Aldred was appointed to the inquiry and supports claims that she has a conflict of interest. I raised these issues in a piece for Index last month.

Aldred is on secondment to the inquiry from her role as deputy head of the foreign and defence policy secretariat at the Cabinet Office, where she had extensive involvement in Iraq policy.

Her appointment was announced on 6 July 2009 but she did not take up the role full-time until that September. On 15 July, two weeks before inquiry chairman Sir John Chilcot formally launched the inquiry at a press conference, Aldred briefed a US diplomat about its plans.

According to the leaked cable, Aldred briefed the official on the timing of the inquiry’s report, which she said “could not come out before the end of July 2010”. Having disclosed the inquiry’s plan to visit Washington, she “noted that the committee would not have subpoena powers in the United States [and] promised to coordinate the committee’s planned travel with embassy London.”

Aldred’s Cabinet Office expense claims shows that she flew to Washington in late May 2009, two weeks before Gordon Brown announced the inquiry, for “UK/US discussions”.

A previously leaked US embassy cable from September 2009 revealed that a British civil servant told a US state department official “that the UK had “put measures in place to protect your interests during the UK inquiry into the causes of the Iraq war”.

This assurance was given at the time Aldred took up her role as inquiry secretary. The inquiry has suggested that the civil servant was referring to a controversial Cabinet Office protocol on sensitive information. This was recently used to stop the inquiry publishing records of what Tony Blair told US president George Bush in the run-up to the war. It has also disclosed that the protocol was negotiated with the Cabinet Office by the inquiry secretariat, of which Aldred is head, before it was seen by the Chilcot committee and was then signed by Aldred.

Plaid Cymru parliamentary leader Elfyn Llwyd, who raised concerns over Aldred’s position in a Commons debate two weeks ago, told me: “This new revelation confirms my view that Margaret Aldred’s position is untenable. She is clearly unable to separate her role at the Cabinet Office from her highly sensitive position at the inquiry.”

Ed Davey, formerly a Liberal Democrat foreign affairs spokesman and now a Business Department minister, said Aldred’s appointment “raised serious questions” about the inquiry’s independence.

A spokesman for the Iraq Inquiry told the Telegraph that the chairman, Sir John Chilcot, and his colleagues were aware of Mrs Aldred’s role as deputy head of the Foreign and Defence Policy Secretariat. He said “The committee is satisfied that its procedures are capable of ensuring balance in its work.”