Police investigating the cash for peerages scandal will use American software to search for deleted emails on Whitehall computers, according to press reports.

Pasadena-based Guidance Software confirmed that it had provided the computer program. 

"We have supplied this regulatory software to Scotland Yard and it is currently being used in the cash for peerages investigation," Tim Leehealey, executive vice president of business and corporate development at Guidance Software, told The Guardian.

"This is a more sophisticated version which can also interrogate individuals' computer hard drives without them realising that this has happened."

John Yates, deputy assistant commissioner at the Metropolitan Police, said that Scotland Yard had already begun the search to try and find any link between the offer of loans and the awarding of honours. 

The program will scan computers and identify any deleted emails between civil servants and Whitehall, including communications to and from Downing Street. 

The cash for honours issue was first raised when four people put forward for peerages were found to have loaned money to the Labour Party. 

The police investigation will also look into 20 Conservative Party backers who loaned money to the party. 

Police had previously removed around 1,000 documents from government departments, including the Cabinet Office and the House of Lords Appointments Commission.