Hundreds of British soldiers are to be sent to Iraq to help the fight against Islamic State, Sky News understands.
They will make up a training mission to assist the Iraqi Army and Kurdish Peshmerga.
The soldiers - expected to number a few hundred - will go to the region "within weeks" senior military sources have said.
The National Security Council is expected to rubber-stamp the mission when it meets on Tuesday.
Although small groups of British troops have conducted similar missions over the past few months, this will be much greater in size and on a more permanent basis.
It's believed the mission will be largely split between the capital Baghdad and Irbil in the Kurdish controlled north.
It hasn't been confirmed which regiments the troops will be drawn from.
The UK government has repeatedly insisted that any such training mission would not constitute 'boots-on-the-ground' although British Special Forces are operating in the region.
In October a dozen soldiers from The Yorkshire Regiment were dispatched to Irbil to train the Kurds to use heavy machine guns.
A Ministry of Defence spokesman wouldn't confirm the specifics of the latest mission but did say: "The Defence Secretary announced the intention to provide further training to the Iraqi military in early November.
"No decisions on troop numbers, units or locations have been made, so this is purely speculation at this stage."
The British contribution will fit into a wider mission involving a number of nations.
Earlier this week, the most senior US Commander Lt Gen James Terry revealed that the coalition training mission would involve around 1,500 soldiers.
Germany recently pledged around 100 soldiers to help train the Peshmerga in northern Iraq. That mission, if approved, will begin early next year.
NATO has also said it would explore options if the Iraqi government came forward with an official request.
The Alliance said that any training mission wouldn't necessarily be based in Iraq. Neighbouring Jordan has been used for similar projects.