Britain and America “profoundly” underestimated the chaos that would be unleashed by the toppling of Saddam Hussein, Tony Blair has admitted, in one of his starkest expressions of regret over the Iraq War.

With the long-awaited Chilcot Inquiry report into the war due to be published within weeks, Mr Blair said that the West had not foreseen the “forces of destabilisation” that fill the vacuum left by the dictator’s fall.

However, he offered no apology for the intervention to topple the Iraqi dictator, and suggested that the West should be prepared to put boots on the ground in the Middle East again if it wanted to defeat Isis.

Speaking at an event hosted by Prospect magazine, the former Prime Minister said: “We underestimated profoundly the forces that were at work in the region and that would take advantage of the change once you topple the regime.

“That's the lesson. The lesson is not actually complicated, the lesson is simple - it's that.

Tony Blair: A career of controversies Show all 11 1 /11 Tony Blair: A career of controversies Tony Blair: A career of controversies The Tony Blair 'selfie'.. A journalist takes a picture of Kennard Phillips 'Photo Op', depicting Prime Minister Tony Blair taking a 'selfie' in front of an explosion in Iraq, during a press viewing of the exhibition Catalyst: Contemporary Art and War Tony Blair: A career of controversies Protesters pictured outside the QEII Conference centre in London in 2011 as former British PM Tony Blair give his evidence in the Chilcot Iraq Inquiry Tony Blair: A career of controversies David Lawley-Wakelin, who disrupted Tony Blair’s testimony at the Leveson Inquiry by bursting into the court Tony Blair: A career of controversies Blair giving evidence Tony Blair: A career of controversies Tony Blair visiting troops in Iraq in 2007 Tony Blair: A career of controversies Blair meeting with troops in Basra, Iraq in 2003 Tony Blair: A career of controversies Britain's Prime Minister Tony Blair speaks to British soldiers at Divisional Headquaters in Basra, May 2007 Tony Blair: A career of controversies British Prime Minister Tony Blair eats dinner with British troops in Basra, Iraq, 21 December, 2004 Tony Blair: A career of controversies Syrian president Bashar El Assad during his official visit to the United Kingdom in 2002. Mr Blair tried to engage Mr Garcia in a conversation about Syria. The former Prime Minister made clear he was very much in favour of military intervention last summer. Tony Blair: A career of controversies Syrian president Bashar El Assad and wife Asma during their official visit to the United Kingdom in 2002. Mr Blair tried to engage Mr Garcia in a conversation about Syria Tony Blair: A career of controversies Former Prime Minister Tony Blair's signature adorns a program he signed for an Iraq veteran during a reception at the Guildhall in London following the service of commemoration at St Paul's Cathedral honouring UK military and civilian personnel who served in Iraq

“It's that when you remove a dictator, out come these forces of destabilisation - whether al-Qeada on the Sunni side or Iran and its militia on the other side.”

However, he suggested that the Middle East would not be better off today were Saddam Hussein still in power.

“There is a line today that's very common in western discourse, left and right, that says 'you know what, it would be better that these dictators stay in power',” he said. “I don't personally agree with it, but it doesn't matter if I agree with it or I don't. Wat the Arab Spring shows you is these countries with young populations, with radical forces operating within them, are not going to accept that.”

Mr Blair did not comment on the Chilcot Report, which is due to be published in July, but his comments give a strong indication of his likely response to its findings. The report is expected to be particularly critical of planning for the conflict’s aftermath, which saw Iraq descend into a bloody civil war, incubating the extremist forces which went on to establish Isis.

Mr Blair said that defeating the group, which controls major cities and swathes of territory in both Iraq and Syria, could require Western ground forces supporting local troops.

“You have got to defeat these people on the ground,” he said. “The armed forces of America, the UK, France, other major countries have both experience and capability so even if we are using them in support of local forces, you have just got to decide what our objective… Is our objective to defeat this enemy? My answer to that is yes.”

He said that Western governments needed to be “honest with our public” about what it would take to defeat the group.

“In my view, defeating them is absolutely fundamental because if we don't defeat them they are going to come and attack us here. This is not someone else's fight, it is our fight as well,” he said.

The former Prime Minister fears Isis may get a stranglehold on Libya (PA)

He said it was important that Libya was not ceded to the militant group, and that if they were not dealt with “they will come and attack us here”.

“We cannot afford to have Isis govern a large part of Libya – we shouldn't be in any doubt they need to be taken on on the ground,” he said.

Ground forces currently fighting Isis in the Levant are mostly Kurdish, Iraqi government, Syrian government and other militant groups.

In Libya, where the group controls the central port city of Sirte, domestic Libyan forces have contained its advances beyond that area.

The UK is currently involved in a coalition of nations conducting air strikes against the so-called Islamic State in Syria and Iraq.

Isis has been losing ground in the Levant in recent months, with Iraqi government forces now advancing on the city of Fallujah, which the group holds.

Mr Blair has previously called for Western ground forces to be used against Islamist militant groups. In an article for The Sunday Times in March he said they were “necessary” to beat Isis.

“We must build military capability able to confront and defeat the terrorists wherever they try to hold territory,” he wrote at the time.