Any civil servant required to work equally closely with Tony Blair and Gordon Brown faces the challenge of reconciling their conflicting demands. But Lord Turnbull of Enfield, the former cabinet secretarywho pulled off that balancing act over much of the past decade, never lost his air of unflappability.

The man whose trenchant comments made headlines yesterday was permanent secretary at the Treasury - its top civil servant - for most of Mr Brown's first term as chancellor. Lord Turnbull went on to serve as cabinet secretary - head of the home civil service - throughout most of Mr Blair's second term.

At the Treasury in the late 1990s, he had the task of smoothing relations between the close-knit clique around Mr Brown and the rest of the departmental machine.

Tall, quietly spoken but with a mischievous sense of humour, this 62-year-old Spurs supporter is from the Rolls-Royce school of mandarins. Lord Turnbull has a disarmingly informal manner. But one is left in little doubt that, behind his round spectacles, there is a formidable brain.

Lord Turnbull's early career saw him exposed to some of the most dramatic events in recent British history. He was private secretary to Margaret Thatcher at the time of the IRA Brighton bomb. He was a senior Treasury civil servant on Black Wednesday - September 16 1992 - one of the biggest crises to have faced Britain's postwar economic system. Afterwards, he went on to become the Treasury official in charge of public spending when Michael Portillo was his ministerial boss.

As cabinet secretary, he played a critical role in fashioning public service reforms. Lord Turnbull instinctively understood the need for the public service overhaul that Mr Blair and Mr Brown put into effect in Labour's second term.

In particular, he helped Mr Blair understand that the civil service could not be reformed by setting targets from the centre. Instead, it was necessary to sustain improvements across the public sector by entrenching greater choice and diversity in health and education - an approach at the heart of what Mr Blair has sought to achieve.

Lord Turnbull will be embarrassed by the public disclosure of his private thoughts. He berated Sir Christopher Meyer, former ambassador to Washington, for publishing details of his official work in a memoir. He wondered what thought Sir Christopher had given to the effect of "patronising and derogatory comments in relation to elected politicians whom an ambassador has been paid - and paid handsomely - to serve".