They are done late at night and without fanfare, a solemn token of prime ministerial respect for the families of those who have fallen serving their country. Ever since Margaret Thatcher wrote handwritten notes to the relatives of the 255 Falklands dead, her successors have followed suit and committed a few thoughts to paper each time a death in service is announced.

The process is regarded as private, the letters are not intended for publication and the subject rarely spoken about in public by officials. Surprisingly, the military high command are cautious about the practice — worried about which families should receive a letter from a senior politician.

Although rare, this is not the first such condolence letter to be made public. The mother of Fusilier Gordon Gentle, killed in Iraq in 2004, released Tony Blair’s letter to her in protest at the six weeks it took to be sent.

The contrast between Gordon Brown’s notes and Mr Blair’s highlights a divide in their approach to the bereaved. Unlike Mr Blair, Mr Brown does not invoke God in his letters nor attempt to justify the military campaign. In saying “I know that words can offer limited comfort at a time of grief”, Mr Brown is implicitly accepting the futility of his own gesture. Mr Blair, by contrast, was defensive even in this most private of missives, telling Mrs Gentle the invasion of Iraq was “vital”, adding “at least I hold this belief sincerely”.

In another letter to be made public, to Reg Keys, father of Royal Military Policeman Tom, Mr Blair wrote that his life had been “lost in a just and important cause, for which future generations would be grateful”.

There is considerable sympathy for Mr Brown’s error among those who have worked closely with former prime ministers. “They take considerable time over these letters. It’s wrong to suggest they are just dashed off — a lot of feeling goes into what they write,” said one former aide.

No error in such a letter is likely to be easily forgiven by the wider public. But nothing will compare with Donald Rumsfeld, the former US Defence Secretary. In 2004, it was revealed that he used a machine to imitate his signature, “in the interest of ensuring expeditious contact with grieving family members”. After an outcry, the practice ceased.

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