ALEX Salmond’s hopes of having former Prime Minister Tony Blair face international criminal proceedings over Britain’s involvement in the Iraq War have hit a legal hitch, it has emerged.

The SNP’s foreign affairs spokesman has revealed he wants Mr Blair to face an investigation by the International Criminal Court if the Chilcot inquiry finds that he made a commitment to US president George Bush to support the invasion.

He intends to reassemble a cross-party parliamentary group that launched a campaign to have Mr Blair impeached 10 years ago to make plans for action before Sir John Chilcot’s report is published in July.

The former First Minister said he believed a door could be open for a criminal investigation with the ICC under the offence of "crime of aggression".

But the ICC said that the crime of aggression is “currently not within the ICC jurisdiction, so no preliminary examination can be conducted based on this specific crime”.

The ICC defines a crime of aggression as a “crime committed by a political or military leader which by its character, gravity and scale constituted a manifest violation of the [United Nations] Charter”.

The ICC confirmed the court may, in future, exercise jurisdiction over the crime of aggression. A decision on the matter is due to be made by its members after January 1 next year.

The ICC is currently looking into Britain’s conduct during the conflict, but not whether the decision to engage in armed conflict was legal.

Read more: Alex Salmond reveals plan to put Tony Blair in the dock over Iraq War

The "crime of aggression" is contained within the Rome Statute, the treaty that stablishes the court’s functions, jurisdiction and structure.

However, an ICC report, in examining the allegations over the legality of Britain’s involvement in the Iraq War 10 years ago, says that the court may not exercise jurisdiction over the crime until a provision has been adopted which defines it and sets out the conditions under which the court may exercise jurisdiction.

“This arrangement was established because there was strong support for including the crime of aggression but a lack of agreement as to its definition or the conditions under which the Court could act,” says the report by Luis Moreno-Ocampo, then chief prosecutor of the International Criminal Court.

He confirmed then that he had no mandate to address the arguments on the legality of the use of force or the crime of aggression.

Mr Salmond, – who led SNP MPs in voting against war in the House of Commons in 2003 – said he believes the Chilcot report will reveal that Mr Blair committed Britain to joining the US-led military action in private conversations with Mr Bush.

The ICC in the Hague has been a part of the global justice system since 2002, and the Rome Statue which established the court has been ratified by over 120 countries, including the UK, but not the US.

It is seen as a court of last resort, intervening only when national authorities cannot or will not prosecute.

Mr Salmond said he favoured the ICC route but was “open to Mr Blair being held to account on whatever is the best way”.

“My own view is that if Chilcot finds, as I hope and believe he shall, that Blair pre-committed to war in Crawford Ranch in 2002 which is what I’ve always believed the evidence points to, in my view everything that happened after that was a fabrication in order to provide a justification for a decision that had already been made, “ he said.

Read more: Alex Salmond reveals plan to put Tony Blair in the dock over Iraq War

“If the Chilcott report finds that causal link then that would in my view provide the body of evidence and therefore it would be up to a group of citizens to take this evidence to the office of the prosecutor of the ICC and ask him or her to investigate.

“My own view is the ICC is a better route. And what would be the crime? The crime would be the crime of aggression.”

Mr Salmond played a major role in the impeachment group, formed in the main by Welsh and Scots nationalist MPs before he became First Minister - and at a time when the SNP were a minor party in Parliament with just three MPs Now the SNP with 54 MPs are the UK’s third biggest party.

The reassembling of the impeachment group comes ten years after a chain of events it set off led to Mr Blair’s government avoiding a bloody nose on the Iraq war in a House of Commons vote.

The International Criminal Court has already begun a preliminary inquiry into allegations that British troops were responsible for a series of war crimes after the invasion of Iraq.

The ICC has previously come under heavy criticism, particularly from the African Union (AU), for disproportionately targeting Africa.

In its 13 years till September, 2015, the court had only charged African nationals,

Of the 29 cases before the ICC in September, 25 were from the Eastern and Central African region - a list that not only includes rebel leaders and senior military generals, but also a former vice president, a current vice president and a sitting head of state.

Uganda had three cases before the court at that point with Joseph Kony, the warlord responsible for abducting tens of thousands of children being one of the most high profile individuals to be charged. He is facing 33 counts of crimes against humanity and war crimes committed in Uganda since 2002, but he is understood to be still at large since his arrest warrant was issued in 2005.