HM Revenue and Customs has offered a £20,000 reward for information that leads to the recovery of the two CDs and data on 25 million people that are at the centre of Britain's biggest ever data breach.

Chancellor Alistair Darling has already announced a review of the HMRC data loss fiasco - to be led by Kieran Poynter, chair of PricewaterhouseCoopers - which is set to report on the "exact circumstances" surrounding the debacle by the middle of this month.

But police are still searching for the missing CDs. The reward was offered alongside a police appeal to thousands of staff working at HMRC, the Treasury and the National Audit Office - the intended recipient of the two CDs containing personal and bank details of millions of child benefit claimants and their children. Staff are being urged to check both at work and in unspecified 'other locations' to see if the missing discs can be found.

Staff are also being quizzed by TNT, the courier firm that handles the government's internal post.

A core team of 32 detectives from the Metropolitan Police specialist and economic crime command, including computer experts, are at work on the case, alongside officers from Northumbria, Greater Manchester, Strathclyde and Leicestershire constabularies.

Scotland Yard said its inquiries included the forensic examination of various computers in order to verify witnesses' accounts of the events surrounding the data loss.

In a statement, the Met Police added: "The enquiry has been particularly challenging due to how common compact discs are within offices, the number and size of the offices requiring searches and the number of organisations where the package may have travelled through."

There was still no evidence that the data had fallen into the hands of criminals, the police confirmed.