Gordon Brown has now written to all the families whose loved ones have been killed in action since he came to power, Downing Street said today.
The Prime Minister apologised and ordered a review today after it emerged that relatives of Territorial Army Trooper Jack Sadler did not receive a letter of condolence when he died in 2007.
The review quickly established that Trooper Sadler's letter was one of three which went unsent that year, but Mr Brown's spokesman was unable to say whether any similar cases had been uncovered relating to deaths in 2008 or 2009.
He told reporters: "To the best of our knowledge, all letters have been written and either have been, or are in the process of being, dispatched."
The review, by 10 Downing Street's most senior civil servant Jeremy Heywood, will be completed "as soon as possible", said the spokesman.
Trooper Sadler died in December 2007 when his vehicle hit a landmine in Helmand Province, Afghanistan. His father, Ian Sadler, from Exmouth, Devon, said he only received his letter of condolence last month.
Speaking to BBC Radio 4's The Report, Mr Sadler said: "Jack was killed on December 4, 2007, and I received a letter of condolence from the Prime Minister with no date on it on November 17, 2009.
"I have a letter apologising, not from the Prime Minister, but from Jeremy Heywood, who is his permanent secretary, apologising that an administrative mistake resulted in my not receiving a letter from the Prime Minister.
"It's not good, is it? Nearly two years later and the PM hasn't apologised, just his aide."
Mr Sadler added: "It goes to show what this present administration thinks of our soldiers."
Mr Brown apologised for the oversight when he appeared at a press conference in Downing Street this morning.
"As you know, I write personally to every family, and where there has been an unacceptable error, for which I apologise unreservedly, and a letter has not been sent, I have been made aware of this," he said.
"I wrote to the relevant families immediately and expressed my condolences.
"I've also ordered an urgent review to ensure that any other cases were identified and we can make sure that this did not happen again.
"I can only apologise to those families, and I want to send my heartfelt condolences to them.
"They have my profound thanks for the invaluable contribution that their loved ones have been making to make Britain safe and I understand their grief and their sadness at a time when they have lost so much."
Mr Brown's spokesman told reporters at a regular daily Westminster briefing: "We apologise unreservedly for any errors where they have occurred.
"Clearly the Prime Minister does this because he thinks it is the right thing to do and believes that prime ministers should write to any family where they have suffered a fatality."
Despite repeated questions, he did not say whether the letters currently in the process of being dispatched included any from 2008 or 2009 which have been subject to delays.
Today's apology comes after Mr Brown was criticised last month by Jacqui Janes, the mother of a dead serviceman, after he misspelt her son's name in a letter of condolence.Reuse content