Tony Blair's decision to invade Iraq was a costly episode

Tony Blair's decision to send British troops to invade Iraq was controversial from the start. Photo: Press Assocation

He did it successfully in the Balkans. A military intervention which forced a brutal leader to stop abusing large swathes of his population with minimal loss of life.

He did it too in Sierra Leone in 2000. A short, sharp operation which epitomised the military doctrine at the time called "Go First, Go Fast, Go Home."

Tony Blair's plan was to do it again in Iraq: an quick invasion to remove the threat posed by Saddam Hussein's supposed Weapons of Mass Destruction.

Controversial from the start and launched despite critical voices from leaders in many world capitals, the plan successfully toppled a brutal dictator.

A British Warrior armoured combat vehicle drives into a picture of Saddam Hussein in the city of Basra in March 2003

But it left a country at the mercy of terrorists, the British forces based there in the aftermath dangerously exposed, and the reputation of a Prime Minister at home badly damaged.

The decision by Tony Blair, a man who favoured an interventionist role in the world for Great Britain, affects the decisions taken by political leaders today.

It was costly episode, both in treasure and blood, but the consequences of the Iraq invasion are felt today: a reluctance, for example, to intervene in Syria now - despite the similarities with the situation in Iraq, a decade before.

Different times, different occupants of the White House and Downing Street.

Prime Minister David Cameron with US President Barack Obama Credit: REUTERS/Jason Reed

The consequences of Iraq were felt too in Libya - where David Cameron led the international effort to protect the citizens at risk from attack from Muammar Gadaffi - but where he also shared the widespread hesitation to send in ground troops.

Iraq might have been much less costly in terms of British military lives lost than Afghanistan (179 in Iraq versus a current total of 440 in Afghanistan) but ultimately it was the Iraq invasion which set in motion a decade of conflict for British forces - one that has yet to come to a close.

The UK pulled its troops from Iraq in 2009 but we are still two years away from withdrawing combat troops from Afghanistan. At the peak we had 12,500 troops spread across two dangerous battle zones in two unstable countries.

It stretched the British military almost to breaking point. Commanders warned again and again they couldn't sustain that double deployment for very long.

British troops on an operation in Helmand province, Afghanistan in 2009. Credit: British troops on an operation in Helmand province, Afghanistan in 2009.

And with Iraq now behind us and an end in sight in Afghanistan - Britain is unlikely ever to see an invasion on the scale of Iraq again. Recent cuts to personnel numbers have left the UK with the smallest army since Victorian times.

So we may well look back on Iraq as the last big invasion for our Armed forces. And although political leaders will embark on military deployments in the future and decide whether or not to send British soldiers, sailors and airmen into harm's way - they are unlikely ever to be of the same size.

And any such operation will most likely be shared with our Allies (increasingly the French, not the Americans).

The view in Washington under President Obama is that preventative conflicts should now be the last resort - not the first resort as it was a decade ago.

Tony Blair and US President George Bush holding a joint conference on Iraq in 2003. Credit: Reuters/Mike Theiler

In short, British Prime Ministers will not be able to do it in the way in which Tony Blair did it then.

And nor are they likely to do it with the same determination as Mr Blair - a man for whom ten long years in office is still principally remembered for his decision in 2003 to stand shoulder to shoulder with George W Bush and to send British troops to invade Iraq.