A lack of Whitehall cooperation has prompted the parliamentary ombudsman to contemplate resignation.

In her annual report, Ann Abraham said that her office was continuing to experience difficulties when investigating sensitive political issues.

She said that difficulties experiences in recent years when it came to investigating complaints under the Code of Practice on Access to Government Information were still continuing.

Abraham said that "a number of my investigations have been seriously delayed" as a result.

The main difficulties were identified as departments failing to respond within reasonable timescales and a reluctance in a small number of cases to provide the actual information forming the subject of the request.

"These problems led me to consider whether or not I could properly continue with this work," the ombudsman warned.

"I noted that in previous reports my predecessor had to raise the possibility of withdrawing from the role of monitoring the Code in the face of a continuing lack of co-operation from departments.

"I fully recognise that, in many of the cases involving the Code, I am dealing with material of considerable political sensitivity about which I have often to make finely balanced judgments in respect of its potential release, but I cannot be expected to carry out my responsibilities properly with one hand tied behind my back."

In a bid to end the impasse, Abraham said she had held talks at the "highest level" with the Cabinet Office and the Lord Chancellor's Department in a bid to agree a memorandum of understanding between the ombudsman and Whitehall departments.

"If this does not prevent a repetition of the problems we have been experiencing, I shall need to consider whether I can properly continue with this work," she said.

Two key investigations were blocked by Whitehall using statutory provisions of the Parliamentary Commissioner Act 1967.

In the first the Cabinet secretary certified that the information sought about the development of policy leading up to the Human Rights Act 1998 related to the proceedings of a Cabinet committee and therefore could not be provided to the ombudsman.

In the second the Cabinet Office issued a notice informing the ombudsman that it would be contrary to the public interest to disclose information relating to potential ministerial conflicts of interest under the Ministerial Code of Conduct.

This was the first time such a notice had been issued in respect of a Code investigation.

A complainant had sought information on how many times ministers had consulted departmental permanent secretaries on potential conflicts of interest and what action had followed as a result.

However, the departments failed to provide any information, resulting in a complaint to the ombudsman.

But as Abraham investigated the issue she received on June 25 a notice in writing signed both by the secretary of state for constitutional affairs, Lord Falconer, and Cabinet Office minister Douglas Alexander stating that releasing the information "would be prejudicial to the safety of the State or otherwise contrary to the public interest".

As a result of the notice, believed to be the first to be issued in living memory, the ombudsman was forced to halt her investigation into the complaint.