Lord Goldsmith has said he will not step aside from his role in the cash for peerages investigation, despite fears over a conflict of interest.
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 himself have led to concerns from opposition parties that his role in this case could be considered a conflict of interest, possibly undermining the inquiry.
Shadow home secretary David Davis said it would be "improper" for Lord Goldsmith to be consulted.
"This is a unique situation and it would be improper for the CPS to refer in any way to any political appointee," he said.
Scottish National Party (SNP) MP Angus MacNeil, added: "It is with some alarm that I hear the attorney general is to involve himself with a matter where there is such an obvious conflict of interest. He must instead publicly declare he will maintain a healthy distance, as would befit anybody with a political relationship with the prime minister."
However, the attorney general said: "I have always made decisions in the public interest, in the interests of justice and absolutely independently out of apolitical interest.
"I think we need to wait to see whether the police produce a file for the Crown Prosecution Service, what it is about and what issues there are to consider," he told the Bar Council's annual conference this weekend.
The decision to remove himself from the inquiry rests with Lord Goldsmith, but his cabinet colleagues have hinted that he may well step aside.
Constitutional affairs minister Harriet Harman told ITV's Sunday Edition: "I think you can be confident that what the attorney general will do is recognise there has to be public confidence in the fact that the decision will be taken independently and in an open way.
"I'm sure that the attorney general will say how he is going to go about it and he will want to be sure that people respect the office of attorney, that they respect the way that prosecutions are decided on independently and everything is out in the open."
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.