Thursday's recall of Parliament will be the fourth time David Cameron has interrupted MPs' holidays.
- In April, the death of former Prime Minister Margaret Thatcher sparked a full day of tributes in both the Commons and the Lords
- MPs were recalled twice during the 2011 summer recess - first for a statement about phone hacking and the police in July, and then again in August after riots broke out
- Previously, recalls had been relatively rare - the next occasion was a recall in April 2002 to mark the death of the Queen Mother
- Parliament was also recalled three times in the wake of the 9/11 terrorist attacks and subsequent military action
The Prime Minister has said 'the world should not stand idly by' after hundreds were killed in apparent chemical attacks in Syria last week.
Any UK military action in Syria would involve submarine-launched cruise missiles rather than air strikes, a military expert has predicted.