Below are the principles that computer forensic experts in both the police and private sector follow, these come from the ACPO Guidelines.
These principles cover the imaging of the hard drives.
Principle 1: No action taken by law enforcement agencies or their agents should change data held on a computer or storage media which may subsequently be relied upon in court.
Principle 2: In exceptional circumstances, where a person finds it necessary to access original data held on a computer or on storage media, that person must be competent to do so and be able to give evidence explaining the relevance and the implications of their actions.
Principle 3: An audit trail or other record of all processes applied to computer based electronic evidence should be created and preserved. An independent third party should be able to examine those processes and achieve the same result.
Principle 4: The person in charge of the investigation (the case officer) has overall responsibility for ensuring that the law and these principles are adhered to.
Part 35 of the Civil Procedure Rules defines how an expert witness (e.g computer forensics expert) should give evidence in court, produce reports, and what evidence should be given for civil cases