George Trefgarne is a former economics editor of the Daily Telegraph and now runs Boscobel & Partners, a consultancy.

I hesitate to take on the powerful combined forces of the editor of this site, James Frayne and Nick Timothy, but having reflected carefully on the oft-proclaimed thesis that “lower middle class provincial voters are the key to Conservative victory”, I have decided that somebody needs to take it on. And that somebody might as well be me.

I don’t mean to say that it is 180 degrees wrong. On the contrary, there is much good sense in the concept that all Conservatives needs to have as wide an appeal as possible and to get outside their comfort zone.

So I would say that it is a thesis which is half-right, or even mostly right. I said as much in a piece for a rival site when I coined the term Car Share Conservatives (based on Peter Kay’s touching comedy). It can be a powerful motivator to develop genuinely consumer-focused policies, such as encouraging home-ownership or cutting taxes. And it is a useful corrective to the Conservative tendency to default into representing retired City-types from the Home Counties.

But in several important respects this lower middle class thesis is inadequate. It misses certain nuances and subtleties about people, groups and society which means it is self-limiting.

Ordinarily, one would not be that fussed. Much of this is just a reaction to the metropolitan values and background of David Cameron and co. But we have just had an election in which this class-based campaigning was tested and found severely wanting.

Furthermore, because it is a thesis which is embraced unquestionably by too many people, its flaws are in danger of compounding into grotesque election-losing errors.

Its first limitation is that, in principle, class is an insufficient way of describing people. In this case, pollsters rely on the 50-year old definitions provided by the Market Research Society. Here his C1/C2 voters are defined as “supervisory, or clerical, or junior managerial, administrative or professional” and “skilled manual workers.”

As yourself, do you fall into these categories? And if you don’t, do you think the people you know who do, might be happy to be described as such? Is there not more to them than how they currently make a living? Where does a nurse fit in, or an IT worker, or a graduate who happens to be working as a barista? Or a temporarily staying-at-home Mum? Supposing they get a promotion? Do they go up a class? Yes they do. But have they really changed as people? No.

What is more, many people might prioritise their membership of other groups when it comes to their identity. A Scottish Nationalist might, for instance, believe their nationality is more important than their social class. Ultimately, it is for individuals to elect what group, if any, they belong to, and not a patronising social scientist.

Class, as a concept, is one of those things people like to talk about but cannot properly define. It is, when you think about it, a rather poor Marxist way of describing people as it doesn’t capture the fluidity or changeability or individuality of society.

The second limitation is regional. I have noticed that the Conservative proponents of the provincial lower middle class thesis are frequently rather anti-London. They positively revel in disagreeing with people on the basis that “you would say that, you live in London in £1 million house and are totally disconnected with reality” etc etc.

This Conservative anti-London prejudice used to be simply tiresome. Now it is positively dangerous. The Conservative party has been almost eviscerated in London. Battersea, where I live, went from a 7,000 Tory majority to a 2,000 Labour one. I can tell you from my own experience that middle class Londoners – many of whom admittedly voted Remain – are repelled by this sort of rhetoric and positioning. Rightly or wrongly, they have come to loathe Theresa May’s style as the epitome of an arrogant, backward, negative world view which they feel should have been outlawed in the 1960s.

Yet the idea that the Conservative Party can win an election while somehow being wiped off the map in London – the capital city – is surely absurd and certainly without precedent. I have seen forecasts, for instance, which show that the flagship boroughs of Wandsworth and Westminster could be lost in the local elections next year. Surely, we can all see that is disastrous. Hopeless. The road to ruin.

A final point is this: there is something rather negative, divisive and mean-spirited about bringing up class the whole time. It panders to resentments and denies hope, humanity, sympathy, sentiment, optimism, religion, risk and aspiration. Walking around with a chip on your shoulder is not a good look for the Conservative Party.

We should not ignore class as a concept, but by dwelling on it too much we limit ourselves. By banging on about class, you risk adopting the language, mindset, prejudice and philosophy of the enemy. We need a bigger, more generous, up-to-date and agile vision to win an election than an episode of Upstairs, Downstairs, entertaining though it is.