Scotland Yard has been asked to extend its cash-for-influence investigation to cover claims made about four more members of the House of Lords.
Liberal Democrat Chris Huhne wrote to Scotland Yard detectives following allegations in the Sunday Times that further peers broke the law by tabling amendments favouring groups that were paying them.
Assistant Commissioner John Yates is already considering a call from Mr Huhne for formal investigations into Lords Truscott and Taylor of Blackburn - who allegedly told undercover reporters they had tabled amendments for paying clients.
In his latest letter, Mr Huhne said that if the fresh claims - involving Lord Berkeley, Lord O'Neill, Baroness Valentine and Baroness Coussins - were correct they could be guilty of an "offence of bribery or of misconduct in a public office".
All deny wrongdoing and say they declared their interests.
Justice Secretary Jack Straw confirmed at the weekend that he wanted punishments beefed up so that misbehaving peers could be kicked out of the upper chamber.
The measures, being added to the forthcoming Constitutional Renewal Bill, could be retrospective - meaning that they would cover those caught up in the current scandal.
Other disgraced peers with criminal convictions could also face being ejected, including author Lord Archer of Weston-super-Mare and newspaper mogul Lord Black of Crossharbour.
Jeffrey Archer received a four-year prison sentence for perjury and perverting the course of justice, while Conrad Black has been jailed in the US for fraud.
