Air strikes in Syria: what MPs are voting on

Today MPs will vote on whether or not to begin air strikes in Syria, targeting Islamic State. The debate begins at 11.30am and is expected to finish with a vote around 10pm, according to the BBC. It will be streamed live on Parliament TV.

The motion asks MPs whether or not they "support Her Majesty's Government in taking military action, specifically airstrikes, exclusively against ISIL in Syria".

We've previously covered the role of Parliament in approving military action, noting that MPs technically don't have to give the government permission to use force. Politically, though, there is now a convention that the government win a vote like this before acting.

Our legal adviser Joshua Rozenberg gives a similar explanation on the BBC website, going on to discuss the separate issue of whether air strikes are legal in international law.

The government motion mentions and quotes from a UN Security Council resolution condemning Islamic State. This alone doesn't make intervention compatible with international law; the House of Commons Library says that it "seems intended to have more political than legal impact".

The government case is that bombing is legal in self-defence, which we recently wrote about in the context of fatal drone strikes on British alleged terrorists.

Setting aside the legalities, the Economist has compiled a useful summary of the arguments for and against the strikes.

We've been asked about factchecking key claims in this debate. Are there are 70,000 moderate fighters in Syria? Have RAF air strikes in Iraq over the past year managed to avoid civilian casualties?

Like many claims about foreign affairs and defence, these kinds of assertions depend on classified sources, or sources that we can't get at to scrutinise, and so we won't be factchecking the debate.