Lord Goldsmith has said he will appoint an independent QC to advise whether or not to bring a prosecution in the cash for peerages row - if it goes that far.
But the Labour minister said he could not remove himself from the decision entirely.
The life peer's position as attorney general means he should be consulted when prosecuting certain cases, including corruption, under the 1889 and 1906 Prevention of Corruption Acts.
The final decision rests with the Crown Prosecution Service (CPS), but Lord Goldsmith's position as a close ally of Tony Blair and a former Labour party donor have led to concerns from opposition parties that his role in this case could be considered a conflict of interest, possibly undermining the inquiry.
And, after concerns were raised over a conflict of interest, the attorney general last night said he would appoint a senior QC to advise him if the case was to go ahead.
"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," Lord Goldsmith explained in a letter to shadow attorney general Dominic Grieve.
"There are a small number of offences for which any decision to bring a prosecution would require my personal consent under statute.
"In such cases the need for my consent [or that of the solicitor general] is an essential legal condition. It is not one which can be avoided."
Lord Goldsmith, in an attempt to show his position would not compromise the case, said he would consult independent experts on the subject. He also pledged to make sure the reasoning behind a potential decision not to prosecute was fully explained.
"I propose that my office should appoint independent senior counsel to review all the relevant material and advise on any prosecutions," the letter states.
And if the decision is made not to prosecute, then Lord Goldsmith said he would consider "how best to ensure that the basis for that decision was explained".
Police launched an investigation into possible breaches of the Honours (Prevention of Abuses) Act 1925 earlier this year, after claims that Labour was offering wealthy backers a seat in the House of Lords in return for loans.
The investigation has since been extended to the Conservatives, but both parties deny any wrongdoing.