The publication of full details of ministers' private interests, promised by Gordon Brown 18 months ago, has been delayed by the appointment of Lord Mandelson.

Weeks after entering No10, Mr Brown said that all of ministers' relevant financial interests would be released “to ensure proper scrutiny of ministerial conduct”.

But with no sign of the list at the end of last year, the Cabinet Office could say only that its publication was expected “shortly”.

Officials said that last year's reshuffle, in which Lord Mandelson returned to government as Business Secretary, had caused the delay. “Some new ministers have required quite a bit of investigation,” said one source.

Lord Mandelson has so far declared the bare minimum in a voluntary entry to the Lords Register of Interests. He did not, for example, list his links to Oleg Deripaska, the aluminium magnate, who welcomed both the peer, when he was the EU Trade Commissioner, and George Osborne, the Shadow Chancellor, on to his yacht in Corfu last summer.

The ministerial code says that all private interests, financial or otherwise, should be declared to a senior civil servant. Previous interests should be declared where relevant. The updated code adds that, while some personal information will stay secret, “an annual statement covering relevant interests will be published”.

The first list was promised by the man appointed as an independent adviser on ministerial interests, Sir Philip Mawer, the former standards watchdog. He told MPs last February: “It is very important that the public should know what's going on.”

In October the Cabinet Office said that the list would be published after the summer recess, adding that it would provide reassurance that “no conflict exists between a minister's public duties and private interests”.

In a letter to The Times in October the Business Secretary said that he had “met a great number of business people” as Trade Commissioner but would follow the code to avoid the perceptions of conflicts of interests.

A Cabinet Office spokeswoman said it was for Sir Philip to decide how much information about Lord Mandelson's contacts with businessmen such as Mr Deripaska should be published.

“Sir Philip Mawer was appointed as an independent adviser on ministerial interests in January and will be publishing his annual report shortly. The report will take into account ministerial changes resulting from the October reshuffle.”

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