A parliamentary committee criticised the Government today for a "lack of clarity" over whether a House of Commons vote would be needed before the UK supplied arms to opposition forces in Syria.
The House of Lords Constitution Committee said it took ministers "a significant amount of time" before they explicitly committed the Government to allowing MPs to vote on the issue, and said it remained "unclear" how Parliament would be consulted if further military involvement in Syria was planned.
But the committee rejected calls for legislation to give Parliament a formal role in approving any military action overseas.
A constitutional convention has developed since Tony Blair gave MPs a vote on the Iraq War in 2003 which would make it "inconceivable" for a prime minister to refuse a Commons debate on military action or to ignore the result of a vote, the committee found.
These arrangements "seem to be working well" and "the risks and difficulties associated with formalisation outweigh any benefits which it might bring", said the cross-party committee in a report entitled Constitutional Arrangements For The Use Of Armed Force.
Foreign Secretary William Hague told MPs in 2011 that the Government would enshrine in law the requirement for Parliament to be consulted on military action. But Deputy Prime Minister Nick Clegg said in January this year that there was a debate within Government on how this could be done, which remains unresolved.
Today's report found that Cabinet should be "the ultimate decision-maker on whether to use armed force overseas".
A formal requirement to seek parliamentary approval, either through primary legislation or a resolution of the Commons, could create a risk that decisions to go to war would be subject to judicial review in the courts, with damaging effects on morale in the armed forces, warned the report.
It could also have a detrimental impact on the UK's standing if the Prime Minister was unable to be confident that he could deliver on international obligations - such as the treaty commitment to common security with Nato allies.
The committee expressed concern that, at a time when the types of armed intervention and the means of warfare are fluid and constantly changing, a formalised approach could limit military flexibility.
And it warned that the freedom to manoeuvre available to commanders on the ground could be constrained if there was any suggestion that parliamentary approval was needed for any change in the type of action undertaken once an operation is under way.
Committee chair Baroness Jay of Paddington said: "Since our original report into the issue in 2006, a convention has become established that the House of Commons is consulted when military action overseas is undertaken. That is a good approach and to be welcomed.
"However, we do not think that the process should be formalised, as we have concerns that with the changing nature of international conflict any definition would be too hard to draw up.
"We were disappointed that, in the context of the current conflict in Syria, the Government took so long to commit to a Commons vote on any moves to arm the Syrian National Council."