History matters in elections. In this year’s US Presidential contest, political science models based on past relationships – involving, for instance, incumbent popularity or economic growth – did better than short-term modelling based on opinion polls. Most such models predicted a very close race, which could go either way, and in some notable instances predicted a Donald Trump victory. Local election results from the 2010-15 Parliament were the clue that allowed forecaster Matt Singh to predict that opinion polls were failing to pick up the true levels of party support running up to the UK’s 2015 general election.

So if we want to look ahead to the next general election, and for all opinion polling’s recent problems, it is probably still useful to look at where we are now in UK polling. It should be quite a simple job to look at present levels of support for Labour in opposition, and the Conservatives in government, and to project what will happen next based on past experience.

Let’s start with the deficit between Labour’s numbers and those of the Conservatives. Right now, if we take each pollster in the field’s last results at an average, Labour is a long, long way behind – 13 per cent or so. They have never before been so far behind while in opposition at this stage of a Parliament, about 19 months following the previous general election. The closest comparison is the eight points by which Neil Kinnock’s Labour lagged the triumphant Thatcherite Conservative party in December 1988. Oppositions have more often actually led the government in the polls at this point. Even in 1980, with Labour deeply divided, Michael Foot was, in his very early days as leader, able to enjoy an 11-point lead over a very unpopular government struggling with high inflation and unemployment.

When we look at what might happen between now and the next election, an even worse picture emerges. At no time in the modern era, if we take that as meaning the period since 1970, has Labour in opposition gone up in the polls from this point. Between 1993 and 1997, a youthful and popular Tony Blair managed to keep the party's ratings high all the way through to an election - the polling score fell only by 0.4 per cent. But that is the exception. In fact, at this point in Parliament, Labour while in opposition has on average lost 7.2 per cent. After Foot's early boost, Labour split and its polling score plummeted by 19.6 per cent. For today's leaders, this would imply a slump from today's polling of 29 per cent support to 21.8 per cent at the next election.

If those numbers sound apocalyptic, here's a more positive spin. At each general election, Labour has been historically overestimated by polls – by perhaps 1.5 per cent, or a little more. If pollsters’ new post-2015 methods have eliminated this polling error (a generous assumption), then 1.5 per cent or even more of the expected polling "fall" from this point to the next election has already been eliminated. So, if you scrub out that 1.5 per cent fall from my earlier projection, Labour might actually hope to receive 23.3 per cent, or even slightly more. Let’s avoid the perils of false specificity on as generous a basis as we can muster, and round this number up to 24 per cent.

What, though, of the Conservative government’s likely score? Well, at the moment its support hovers around 42 per cent. The honeymoon effect of a new Prime Minister is probably still affecting this rating, although we should also bear in mind that the Conservatives still probably have a lot of scope to soak up Ukip voters if that party does implode. In any case, the evidence since 1970 is that the Conservatives’ vote share at the next general election might be a little higher polling suggests at the moment – by an average of 1.8 per cent or so. Let’s again not be too precise, and call the gain 2 per cent. That would see Theresa May’s party attracting 44 per cent at the polls

The last stage of this analysis is to look at how these very rough figures might translate to numbers in the House of Commons. A result which saw Labour gain 24 per cent, and the Conservatives 44 per cent, would mean on old boundaries a Conservative overall majority of around 150, with 400 seats, while Labour had just about 160 seats. On the new boundaries likely to come into force late in 2018, these shares of the popular vote would again give the Conservatives an absolute majority of perhaps 150, and a total of 375 seats of in a smaller 600-seat Commons, with only something like 150 Labour MPs returned. That would be the party’s worse showing since 1931.

If Labour do indeed receive a score towards the lower end of the 20s, and the Conservatives something over 40 per cent, the next general election will see Labour very badly, indeed historically, savaged. It is possible that the party will suffer a ringing, enduring defeat that will be hard to recover from. It should be stressed that this is a very crude way of looking at these numbers. Labour will probably do better in urban seats, and particularly in London, than this raw data suggests. And in these surprising political times, during which so little seems solid, Labour might somehow be able to escape such a fate. But right now, the historical signs are very, very ominous indeed.

