The "most significant" evidence discovered by police during the cash-for-honours inquiry has not been revealed to the public, according to an official report by one of the senior investigators in the case.
The mysterious claim, which emerged last night, comes days after police disclosed that they had spent £1.4m of public money over a period of 19 months on the inquiry, which resulted in no charges being brought.
Assistant Commissioner John Yates has come in for criticism from Labour MPs for spending so long pursuing politicians over whether or not money was leant to political parties in exchange for peerages.
But the report, leaked to the Press Association last night after it was delivered to the Metropolitan Police Authority, defends the investigation as "focused and proportionate", and discloses that police requested a "forensic image" of Downing Street's computer system.
In November last year, Mr Yates fuelled speculation that he was in possession of critical evidence when he told Tony Wright, the Chairman of the Public Administration Select Committee, that "significant and valuable material" had been obtained. The new claim is likely to fuel speculation that such material remains outside the public domain.
The report also criticises the Electoral Commission for failing to provide "robust oversight" over the definition of a commercial loan.
A Met spokeswoman last night confirmed that the report had been delivered but declined to add any other comment.Reuse content