Blue-sky thinker Lord Birt moves off into the sunset

Tony Blair has lost the services of the man he entrusted with "blue skies" thinking. Lord Birt, the former director general of the BBC, left Downing Street for a job in the private sector yesterday after six years as an unpaid policy adviser.

Lord Birt was the Prime Minister's roving political adviser, looking into selected long-term problems such as transport and energy supply. He said he was leaving "for personal reasons". Asked if anyone would replace him, Mr Blair's spokesman replied: "There is only one Lord Birt."

He will work for Terra Firma, a private equity investment company that owns Odeon and UCI Cinemas and the German motorway service operator Autobahn s & Rast. No10 said that the appointment had been approved under the terms of the ministerial code, but he will be barred from lobbying British ministers and officials on their behalf for a year.

Lord Birt, 61, was highly valued by Mr Blair but ministers and advisers were irritated that he appeared to wield immense influence without being subject to the same rules as a politician or a civil servant. Four years ago Downing Street refused to let him appear before the Commons Select Transport Committee, when he was advising Mr Blair on long-term transport policies.

The committee chairman, Gwyneth Dunwoody, said: "I'm amazed he has been knocking about for six years. We're not entirely clear what he was doing. If people are going to get involved by giving advice to ministers but who are not civil servants, then we have to know how they are accountable."