Standing in for the Queen at an army ceremony, Tony Blair has paid tribute to British troops.

The prime minister was attending a passing out parade for officers graduating from the prestigious Sandhurst leadership training academy.

Blair spoke of his own admiration at the courage, bravery and skill of the UK's armed forces, which he has sent into action more times than any of his modern predecessors.

"Our whole country feels that sense of pride," he said.

He told the assembled officers and their families that their role was "a calling which is noble but one that carries with it very great responsibilities".

"And I know that here at Sandhurst you have been taught all the necessary discipline but also taught that sense of responsibility too."

He warned of the possible need to send the graduates into action in the years to come.

"What you have done here will enable you to fulfil that task in many different parts of the world where you can uphold the values of justice and peace and security," he declared.

Blair repeated his accolade of recent weeks that British forces were the "finest in the world" and paid special tribute to the work that Sandhurst played in that.

"One of the great things about Sandhurst is that those of you who are passing out will serve in the British armed forces but also in the armed forces of many countries around the world," he said.

"And those countries too will benefit from having officers trained at this military academy, trained to the very highest standards in the world and trained to perform their military service with honour and with dignity."

Addressing the wider world picture, the prime minister said the years ahead would be crucial for the military.

"Especially at this time, especially with all the troubles and travails in the world, it is a particular honour to be with you here today," he said.

"When our country has been in danger it is your forbears in the armed forces who have protected us and sometimes it is necessary, much as we loath to do so, to take up arms to defend our country, to ensure justice and ensure security.

"But today our armed forces are called upon to take action in many different parts of the world not so much to defend our country but to defend its long-term security interests."

Blair became just the fourth premier and the first Labour leader to have the honour of standing in for the Queen at the ceremony, joining an elite band that includes only Harold Macmillan, Edward Heath and Margaret Thatcher.