Attorney General Lord Goldsmith says there is "no question" of him standing aside from the cash-for-honours probe.
Lord Goldsmith: Decisions will be taken objectively and impartially
Critics say he is close to the prime minister so he should not be given the right to rule whether or not a prosecution is in the public interest.
But Lord Goldsmith told the BBC that he was the only person responsible to Parliament for prosecutions in the UK.
"Whilst I can't stand aside... I will make sure that... decisions are taken impartially and objectively," he said.
Scotland Yard are investigating whether people have been nominated for honours in return for giving money to political parties.
The probe began after it emerged that some people who secretly loaned Labour large sums before the 2005 election were subsequently nominated by Tony Blair for peerages.
The investigation has since been widened to other parties. All involved deny wrongdoing and there have been no charges.
The Director of Public Prosecutions (DPP) Ken Macdonald has already stepped aside because he is a former colleague of Cherie Blair, while Met Police chief, Sir Ian Blair, who has worked closely with the PM for years has also stepped aside.
As head of prosecutions, the attorney general is usually consulted by the Crown Prosecution Service (CPS) on decisions to prosecute in high-profile and complex cases.
But despite pressure to stand aside Lord Goldsmith - who was given his peerage and job by Mr Blair and is a past donor to the Labour Party - has declined to do so.
Instead he has said, in a written statement last week, that, should he be consulted by the CPS on this particular case, he would appoint an independent senior counsel to review the material and advise him on any prosecutions.
Asked about that stance in his first interview since then, Lord Goldsmith told BBC Radio 4's Today: "There can't be any question of an attorney general standing aside because of the special constitutional and indeed statutory responsibilities that I've got.
"I'm responsible - I'm the only person that is answerable to Parliament - for the prosecutions that take place in this country."
He added: "Whilst I can't stand aside from any involvement in this I will make sure that there are procedures in place which will give confidence, if it ever comes to this, that decisions are taken impartially and objectively.
"And it's my job to make sure that happens. Now we don't know whether it ever will come to it. I don't know if anything will ever come of this investigation. It isn't complete. Let's wait and see."
On Monday the DPP Ken Macdonald told Today that the final decision on prosecutions would be made by senior lawyers in the CPS special crime division.
"The attorney general is entitled to be consulted and they will consult with him and he will no doubt express views about the public interest," he said.