Civil servants can justifiably leak confidential information in "exceptional circumstances", MPs have said.

A report from the Commons public administration committee criticised Whitehall's culture of leaking.

It said the anonymous disclosure of information "damages trust and morale within government", though "no government has seemed able or willing to stamp out this practice".

But it added that "there are exceptional circumstances in which a civil servant could be justified in leaking material in order to expose serious wrongdoing".

"This would need to have followed a failure of proper channels both of disclosure and challenge within government," it said. "In short, it must be a last resort."

The review called for improved and more accessible grievance procedures for civil servants.

Suggested reforms include giving the Civil Service Commissioners the power to report to Parliament any evidence indicating that the government is misleading MPs or the public.

Any case of the civil service refusing to act on a justified complaint should also be reported, said the MPs.

Following recent high profile cases, the committee also examined the role of the police in investigating leaks.

It concluded that the leaking of information should only be a criminal matter where there is a breach of the Official Secrets Act or when there is evidence of serious criminal misconduct in addition to the leak itself.

The MPs said the most effective way of preventing leaks would be to have "accessible, effective and visible ways" for employees to raise their concerns.

"The evidence we received suggests that a high proportion of leaks by civil servants happen because they feel that information is being ignored or suppressed in policy debate," said the report.

"Government departments should foster a culture of vigorous internal policy debate where dissent is encouraged even on the most sensitive of political topics."

Internal leak investigations often fail to find the offender, said the report, with investigations limited by the extent of political leaking.

While special advisers are subject to the same rules on leaking as other civil servants, the fact that only their minister can discipline them means they are "unlikely" to face punishment, said the committee.

The Civil Service Commissioners could investigate alleged breaches leaks by special advisers, and report to Parliament if the minister declines to act on their findings.

"Political leaking is a problem that can only be tackled by a change in political culture," the MPs concluded.

Committee chair Tony Wright said it is "fundamental to good government that civil servants keep the confidences they are entrusted with".

"However, there is a tension between this basic duty and the public's legitimate interest in having access to information about how government works and ensuring government wrongdoing comes to light," he noted.

"It is therefore essential that civil servants know what channels are available to them if they believe there is wrongdoing or information is being suppressed.

"These channels must be timely, effective and, most importantly, not be seen as career-damaging.

"A culture that encourages proper whistleblowing procedures is the best safeguard against leaking, and we believe the civil service has some way to go to achieve this."