Any statesperson should aspire to a personal think tank. Prime Ministers can call on the Downing Street policy unit, while retirees Jimmy Carter, Bill Clinton and Margaret Thatcher have foundations to continue their legacies.

But the main purpose of think tanks is to draw in outside thinking, drive new ideas and keep government thinking fresh, and at a safe distance.

German parties have their own think tanks funded by taxpayers, but in Britain charity law requires they keep a safe and independent distance from party campaigning if they are to enjoy fund-raising tax breaks.

The Smith Institute was set up in 1997, the year Labour took office, in memory of its former leader John Smith, who died three years earlier. The family connection continues, with his eldest daughter, Sarah, now Washington correspondent for Channel 4 News, on its advisory board.

But it is with Gordon Brown that the institute formed the strongest bond. The think tank operates more by organising seminars to draw on others' research than by running its original research programme, and while Mr Brown was chancellor, those seminars kept on turning up in 11 Downing Street. In the year to 2006, it held 27 meetings there, and over 10 years, there were 160 such meetings.

There was little secret of the strong link, with Wilf Stevenson, one of Mr Brown's closest, longtime friends as its director, Ed Balls, the chancellor's closest aide becoming a research fellow while between a Treasury adviser job and election to the Commons.

The Institute of Public Policy Research and Demos, both described as left-leaning' more than Labour-supporting, have played similar roles for Labour.

But for all that Tories complain that charity rules have been broken, their case may be weakened by the widespread perception that Mr Brown has been so short of new ideas since he became prime minister.