In a rare move, British Prime Minister David Cameron has extended an invitation to the acting leader of the opposition Labour party, Harriet Harman, to attend a high-level government security meeting about the threat posed by ISIL.

It has been over two years since a Labour leader has been invited to such a high-level government meeting.

The meeting will be taking place on Tuesday and in attendance will be senior ministers, military chiefs, the head of MI5 and MI6, British intelligence agencies. Labour’s shadow Defense Minister has also been invited.

The move may be a step for the government, which is mulling whether it can garner enough support to extend Britain’s military strikes from Iraq to Syria.

Previously, Labour MPs blocked a vote in parliament to allow airstrikes on Syria. Now that there is a Tory government in office, it is reported that Cameron wants to revisit the plan.

It would be seen as a political blow to have the vote rejected twice, so the government will be reluctant to put it forward without Labour backing.

A government spokesman has said, "The PM thought it was important to ensure the leader of the opposition was fully briefed on the current situation."