Another day, another Labour MP saying something vacuous about immigration. Today's offender is Yvette Cooper, who in an interview with The House says that Labour must make the "progressive case" for ending free movement.

There is a lot to unpick here. The first problem is that the Commons' home affairs select committee, of which Cooper is the chair, is holding an inquiry into public attitudes to immigration right now. That Cooper has already reached a conclusion about it renders the inquiry itself somewhat superfluous.

The second is that Labour MPs need to free themselves from the idea that using the words "progressive argument" is, in of itself, enough to make an argument progressive. There are some things there aren't a progressive argument for, one of which is making people poorer. Any Brexit deal this time takes Britain out of the single market will make people poorer - and you can't stay in the single market without abiding by its four freedoms, which includes the free movement of people.

Cooper attempts to craft a progressive argument by saying that free movement has allowed employers to "undercut wages and jobs". The difficulty here is the evidence that immigration does undercut wages is thin on the ground. It is true, however, to say that capturing the true picture about the bottom end of the income distribution is hard. But it is also true to say in a recession, the people hit hardest are the poor. There is no evidence - literally none at all - to say that anyone being hurt by downward pressure on their wages thanks to immigration is suffering a bigger hit to their wallets than the one they will suffer if Britain leaves the single market.

The third is that, progressive case or no progressive case for it, free movement is going to end, because that is the only way that Theresa May will keep her promises as far as controlling Britain's borders and escaping from the judgements of the European Court of Justice are concerned. Instead of talking about making the case for ending free movement, Labour MPs should do two things: firstly, work out what success looks like for a Britain that is outside the single market. Liberal leavers do have a vision for what that looks like: a Singapore-style economy with worse weather. At present, many Labour MPs have none. The second is to stop talking about ending free movement and talking instead about what immigration rules they actually want, beyond just using the word "control" an awful lot.

But the failure to do that speaks to the big problem with Labour MPs and immigration. When Labour MPs talk about the "progressive case" for ending free movement, what they really mean is the "electoral case": they think the party can't win without ending free movement. They secretly believe that the economic hit and the policy choices that will force upon them will limit the scope of what left-wing governments can achieve - but their alternative is achieving nothing at all. They may be right on the electoral case. They need to start being honest about the economic consequences of that.