The attorney general says he will not bow to pressure to stand aside from the decision on whether to bring charges in the "cash for honours" inquiry.
Lord Goldsmith says he will act in "interests of justice"
Lord Goldsmith said it would be wrong to do so, despite his closeness to Tony Blair, who is expected to face police questions during the inquiry.
But he said he would take independent advice on whether to prosecute.
It came as police and the Treasury refused to comment on claims Chancellor Gordon Brown would also face questions.
The Daily Telegraph said Mr Brown, Deputy Prime Minister John Prescott and other senior Cabinet ministers would all be questioned as witnesses.
Labour officials pointed out early on that Mr Brown, because of his role as Chancellor, had taken no role in party funding.
As head of prosecutions, the attorney general is usually consulted by the Crown Prosecution Service on decisions to prosecute in high-profile and complex cases.
He gives formal consent to proceedings for certain offences, including corruption, where he determines whether it is in the public interest.
But Lord Goldsmith has come under pressure from opposition parties to stand aside from his normal role in the "cash for honours" row, as they say he is too close to the prime minister and the government to rule himself out of involvement.
Director of Public Prosecutions Ken Macdonald - a former colleague of Cherie Blair - and Metropolitan Police Commissioner Sir Ian Blair, have decided to stand aside from decisions related to the investigation.
But, in a letter to shadow attorney general Dominic Grieve, Lord Goldsmith said: "There have been suggestions that I should stand aside from any involvement in this case. However, it would not be right for me to do that."
He said the need for his consent in certain cases was an "essential legal condition" and could not be avoided.
But he added: "If the CPS consult me on a prosecution in this case, I propose that my office should appoint independent senior counsel to review all the relevant material and advise on any prosecutions."
Demands for clarity
If a decision was taken not to prosecute, he would make sure the reasons were explained to "give greater confidence in the objectivity and impartiality of any decision", he added.
Police are investigating whether people have been nominated for honours in exchange for giving donations or loans to political parties.
No-one has been charged but a large number of people have been questioned by police. All those involved have denied any wrongdoing.
Mr Grieve told the BBC he was satisfied with the letter he had received from Lord Goldsmith.
He accepted the attorney general could not abandon his constitutional responsibility but said he could offer reassurances the matter would be dealt with "through advice of an impartial and distinguished, senior lawyer".
He added: "I'm satisfied with that answer and it's the answer which I expected to get"
For the Liberal Democrats, Simon Hughes said it was a "step in the right direction" but was not "clean cut" enough. He said Lord Goldsmith's role should be no more than to formally confirm the advice of independent counsel.
He said: "The cash for peerages investigations go to the heart of the integrity of government.
"Justice can only be done and be seen to be done if nobody with a political role plays any decisive part in any investigation, charge or trial."
SNP MP Angus MacNeil, whose complaint to police sparked the cash-for-honours inquiry, said the letter was "a fudge" and "not good enough".