The launch of the “blog”, disclosed in a leaked letter, is likely to cause concern among colleagues of the communities minister, who fear that he may encroach on their departmental territory.

The letter, circulated around Whitehall by Rory O’Donnell, his private secretary, makes it clear that Miliband intends to address “the policies of other departments” and publicise his views on a range of subjects.

Miliband, a former Downing Street head of policy, is to launch the blog next month providing he wins the agreement of cabinet colleagues.

His spokesman said yesterday that his blog would be an “innovative way” of gauging reaction to government policy, “not racey details of his breakfast habits”.

The blog, a form of internet diary and jottings of thoughts and views, has become popular in recent years. Blogs are informal and allow interaction with people viewing the site.

Miliband’s office declined to release any of his possible blog thoughts last night and it remains to be seen how much interest MPs and the public at large will have in the minister’s musings.

Miliband, who at 40 is one of the younger Blairite ministers, has taken up internet technology before and has participated in online chats on the Labour party’s site.

During one such episode in January he demonstrated a chatty touch when attacking the Tories: “I think TB has given Cameron a hell of a pounding at PMQs [prime minister’s questions] today. The truth is that Cameron’s U-turns are rhetorical so far, but in a way a recognition that Labour has helped shift the political agenda.

“Of course in the end it is substance that counts, and while he is flip-flopping the Tory party has not changed its spots. John Redwood thinking about the future of the NHS — please!”

He is not always so informal. Miliband, who last month was trailing his new idea of “power to the people”, can also happily do jargon.

During the same web chat he told one correspondent: “That’s a good point, Don. I always say, we are seeking the combination of neighbourhood flexibility and strategic leadership and part of strategic leadership is building bridges between communities and not cutting them off so that we make the most of our diverse society.”

Miliband is known for his political pedigree — his father was Ralph Miliband, a Marxist theoretician — and also for his attempts to inject new ideas into government.

While a minister at the education department, he put up a sign over his desk saying “Welcome to a positive thinking zone”.

Miliband has been testing his new blog with colleagues in the Office of the Deputy Prime Minister, but it cannot yet be seen by the general public.

The letter from O’Donnell, dated March 1, shows concern that Miliband might inadvertently break the ministerial code of conduct by talking outside his remit.

“Because, on occasion, David does mention the policies of other departments, for example green or white papers that have been published, I have agreed with the Cabinet Office that I would write to other departments proposing a way of dealing with this issue,” writes O’Donnell.

“I propose that for those cases where he simply mentions the publication of a document by another department saying it is a good thing or words to that effect, there is no need to seek formal agreement.

“However, where his reference goes into more detail this office will contact the relevant private office to agree what is being said.” He said he hoped this could be done quickly.

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