Update: The khat ban passed by 16 votes to two. Full update below.

The Lib Dem rebellion over the ban on khat has opened up the chance of Labour stopping the measure dead in its tracks, but after several months it's still not clear what the party's policy is.

This afternoon there'll be a statutory instrument committee meeting on the ban, which needs to vote in favour of it before it hits the floor of the House for a second vote.

The eight Conservative MPs on the committee will be whipped to support a ban and the two Lib Dem MPs will oppose it. That leaves the seven Labour MPs (and one Jim Shannon) deciding what they're going to do. If they abstain, or vote in favour, it is game over – opponents of the measure probably won't even bother opposing it on the floor of the House. There's only so much anyone can bang their head against a wall. But if they vote against it, Theresa May's plan could be brought to a halt.

Labour is in a bit of a conundrum. Usually it would support any effort to ban a drug. That's just how its brain is wired nowadays. But it may be seduced by the prospect of humiliating the home secretary. Labour MP and home affairs committee chairman Keith Vaz has also lobbied strongly for the ban to be halted.

And the party does has several defences at its disposal, not least of all:

The fact that the drug is as potent as coffee

The fact the ban has no evidential basis to support it

The fact proper consultation has been undertaken, despite the potential for it alienate a large section of the UK's Somali, Yemeni and Kenyan communities

And the fact that prohibition could bolster Islamic terror group Al-Shabab

The Daily Mail report that Lib Dem Home Office minister Norman Baker has washed his hands of the move is accurate. Baker was promoted after the decision had been made, so there wasn't much he could do about it, and now he's distancing himself from it.

The job has been passed on to modern slavery and organised crime minister Karen Bradley to take forward, which is ironic, because there currently is no organised criminal involvement in khat, although there will be if they ban it.

Update: Labour supported the ban. It passed by 16 votes to two.

It was hard to tell for a while. Shadow Home Office minister Diana Johnson accepted most of the arguments against the ban. She accepted that:

The advisory council found no evidence of harm

A ban would lead to racial profiling against Somalis, Yemenis and Kenyans

A ban could not be shown to cause social harms, such as worklessness

A ban could push people from these communities away from counter-terror programmes, like Prevent, as they seek to protect friends from the ban

And yet somehow the party has ended up supporting the ban, albeit with a call for a review in 12 months. That's a policy cul-de-sac. Reviews very rarely tend to scrap the law they are assessing. It's far easier to stop a law in the first place than repeal it later.

So even where Labour admits it cannot show harm from a drug and that a ban may be counter-productive, it still supports it. It would be remarkable if we were not so used to the mania of prohibition.

As Tory MP Mark reckless observed dryly: "Is it the policy of the Labour party that when evidence is unclear on a certain matter it should be banned just in case?"