The human palate can detect five types of flavour: salty, sweet, sour, bitter and umami. The reason why Heinz outsells all other brands of ketchup is it is the only one to perfectly combine all five.

The political palate likewise appreciates five flavours: let’s call them compassion, security , wealth, justice and anger.

Labour's problem that it has lost its ability to appeal to anger: anger directed largely towards immigrants, but also towards welfare recipients, the political class, and foreigners. The problem has been brewing for a long time: it was between 2001 and 2005 that anger over immigration began to eat into the party's vote share, and both Gordon Brown's promise of "British jobs for British workers" and Ed Miliband's mugs promising "controls on immigration" were both failed attempts to fix the problem.

Before the financial crisis, Labour’s ability to appeal to compassion, justice, wealth and security overcame its inability to address anger. Now, Labour is only able to appeal to two of voters’ appetites: for compassion and for justice.

Labour strategists – both inside and outside the leader’s office – believe that if they add a more populist tone to the party platform, they can flip “anger” into their column, and with it, seize back control of the political agenda.

That’s the context for the more critical tone taken on immigration by some of the leader’s allies, the pledge to increase defence spending, and a new video produced by Momentum and the Transport Salaried Staffs Association.

As your rail fares rise again, here's a special message from our friends on the continent...#RailFail #RailRipOff pic.twitter.com/tiiuoVRIdh — Momentum (@PeoplesMomentum) January 3, 2017

Let’s start with the positives: from a technical perspective, it’s one of the best party political broadcasts produced in the United Kingdom, one of the few that could appear on the other side of the Atlantic without embarrassement. It’s well-acted, well-put together, and doesn’t outstay its welcome.

And it achieves its objective: it presents the case for renationalising the railways by appealing not to the usual appeal of justice – privatised railways deliver higher fares and other unfair outcomes – but to anger – privatised railways mean that people abroad receive the benefits of British fare increases.

That’s the good side. Now here’s the bad: its message is that the problem with the way Britain’s railways are run is that they benefit foreigners. (Each of which comes with a helpful accent to aid the viewer in absorbing the message.) It’s as good an argument for letting Virgin run more train services as it is for letting Chris Grayling, the Transport Secretary, or his Labour shadow, Andy MacDonald, run more train services.

It’s also a baffling choice of combination. Support for renationalising railways consistently runs between 55 per cent to 70 per cent in the polls, depending on how the question is phrased, roughly equivalent to the numbers secured for a measure of tougher border control and actually rather higher than the numbers of people who will say they distrust foreigners or support restrictions on their ability to participate in certain transactions. Depending on how that question is phrased, between 11 to 38 per cent of the country admits to some level of distrust towards foreigners, though that varies from outright hostility to preferring a doctor whose first language is English.

If it’s the left’s intention to couple arguments for railway renationalisation with distrust of ordinary Europeans, it should be clear that it may not be support for renationalisation that ends up boosted by the association. The party needs to think more carefully about how it addresses the problem of anger.