The grim milestone that more than 100 UK military personnel have tragically lost their lives in Afghanistan alone since the start of the conflict may, for some, add weight to the argument for immediate withdrawal.

But former head of the British Army, General Sir Michael Jackson, who is set to make an appearance at next month's Buxton Festival, takes a different view – and believes the risks are still worth taking.

"Whenever you set out to intervene in the way we have done, not only in Afghanistan and Iraq, but also in the Balkans, Northern Ireland, even Sierra Leone, it takes a very long time," explained the outspoken ex-military commander.

"You set out to change the course of a nation and it cannot be done in a short time. It takes time and perseverance.

"These people (calling for immediate withdrawal) are not understanding what we are about, which is to take a nation out of the black and give it a stable and much brighter future.

"Obviously there is a cost in blood and treasure, but that is not to say it is not worth doing.

"It is tragic when people are killed on operations, but I believe it is a risk worth taking."

During a military career spanning more than 40 years – from the height of the Cold War to The Troubles in Iraq – Sir Mike has commanded British forces in conflict around the world.

It is these life and times, which feature in his autobiography Soldier, that will be the subject of a captivating one-hour talk and question and answer session at Buxton Opera House on July 21.

But does the man who was once reportedly nicknamed Darth Vader and The Prince of Darkness by his men, and dubbed "Macho Jacko" by the tabloid media, have any regrets?

"It (my career) has been quite a broad canvas and one which I found extremely rewarding. I have been lucky enough to have had a long career and to do something that I love, among the best of company," admitted Sir Mike.

"We are very fortunate to have the quality of people we have in our armed forces. They do a fantastic job with great courage and honour – as well as great humour."

He continued: "I never thought I would finish up as the head of the Army, and it was a great privilege to hold that post.

"The high points of my career have been my command positions on operations – that is what the Army is all about. I have done that at a number of levels. The last time I was in the field was in Kosovo in 1999, which was quite a challenge.

"I suppose the low point is the friends and comrades that I have lost down the years."

As well as serving in Berlin and Northern Ireland, Sir Mike commanded a UN peacekeeping force in Bosnia and NATO's ACE Rapid Reaction Corps in the late 1990s, but it was his leadership of the Kosovo Force – also known as K-For - which saw him awarded the Distinguished Service Order.

He also hit the headlines for famously disobeying the direct orders of American commander General Wesley Clark to intercept Russian forces which had entered Kosovo – resulting in the "Macho Jacko" tag.

Sir Mike's appointment as operational head of the British Army came in 2003, two years after the first deployment of troops to Afghanistan – but only one month before the start of the Iraq war.

Few then expected British forces to still occupy the war-torn Middle Eastern countries they do today, yet Sir Mike believes withdrawal can only be carried out under the "right circumstances".

"The question is at what point do the Iraqis and the coalition come to a joint agreement that what needed to be done has been done, and the Iraqi forces are able to stand on their own. That time will come, but only when the conditions are right," he said.

And will the political problems in the western world over the Iraq invasion mean the end of military intervention in the future?

"It must not, because each set of circumstances must be judged on its merits at the time, and the advantages and disadvantages at the time of deciding which course of action to take," he added.

'Soldier: A Life in the British Army' with General Sir Michael Jackson will take place at Buxton Opera House on July 21 at 10.45am. Tickets, priced £9, are available from the Buxton Festival Box Office on 0845 127 2190.