The House of Lords is to publish a report into the actions of four Labour peers alleged to have been willing to change laws in exchange for cash.
Two Labour peers face suspension from Parliament for six months after being found guilty of misconduct.
The allegations, which Lord Truscott, Lord Snape, Lord Moonie and Lord Taylor all deny, were made by the Sunday Times following an undercover investigation.
Ex-trade minister Lord Truscott and Lord Taylor of Blackburn were accused by the Sunday Times of being willing to change laws in exchange for cash.
If found guilty of misconduct, the four men could face sanctions including suspension from Parliament for a year.
The two men denied the allegations but they now face sanctions following a probe by a House of Lords Committee.
The police decided not to proceed with a criminal investigation into the case.
Labour's leader in the House of Lords had described the allegations against them as "very serious".
'Serious allegations'
The Lib Dems had referred the matter to Scotland Yard after an investigation by Sunday Times journalists, posing as lobbyists, raised questions about the peers' conduct.
Describing the allegations as extremely serious, Baroness Royall - Labour Leader in the House of Lords - asked a sub-committee on members' interests to investigate them.
In its report, the Lords Privileges Committee is expected to say whether the four peers broke parliamentary rules and, if they did, what penalties they should face.
Any sanctions would have to be approved by all members of the House in a vote.
The Sunday Times claimed the four men discussed being paid for amending laws in Parliament.
If proven, this would have been a clear breach of parliamentary rules - which state peers should not seek to influence legislation in return for money.
The Sunday Times released details of conversations Lord Truscott and Lord Taylor had with their reporters in which they discussed what help they might give them and how parliamentary procedure worked.
The men said that, at no time, did they discuss accepting money into return for amending laws.
The Met looked at whether there were grounds for an investigation into the possible offences of bribery and misconduct in public office.
It said its decision not to proceed was taken after considering the prospects for obtaining evidence and whether an inquiry constituted the best use of police resources.
In reaching the decision, the Met said it had taken into the account the fact the Lords would be mounting its own "robust" investigation into the peers' conduct.
