That nice young lad, Owen Jones, does seem to need a little education in matters economic. For example, here he is stating that the closure of the Cornish tin industry impoverished that county:

De-industrialisation is often seen as a northern trauma, but it is not so. The disappearance of tin mining impoverished Cornwall, leaving it one of the only regions eligible for special financial assistance from the EU.

We find it really remarkably difficult to see how that could be true. The Cornish tin industry was only of the most marginal importance after WWII and the decline had firmly set in by the 1920s. And Cornwall today is markedly richer than the Cornwall of pre-WWI when the tin industry was in its pomp. So, given that the closure of the tin industry is correlated with the place becoming richer it's very difficult indeed for us to see how the closure of the tin industry impoverished the place.

There has been a change in relative welath, this is true, but going from being a comparatively rich part of the country to being a comparatively poor one is not the same as becoming poorer or impoverished. Jones is making the mistake of seeing everything in relative terms here instead of absolute.

And as to why the industry changed, that's simple. At the time, and with the available technologies and geological knowledge of the world mining for tin in Cornwall added great value. That is why it was done. Then, with the discovery of easier to access ores (the alluvial deposits of SE Asia as one example), the increasing depths of the Cornish mines and changes in the tin price Cornish mining stopped adding value and became a destroyer of the collective wealth. So it stopped happening: that's exactly why the area is richer today without tin mining that it would be today with tin mining. Because people have moved away from an activity that no longer adds value to other occupations that do add value. And so does the human species become ever richer, as we move capital and labour from low (or in this case, value destroying) activities to higher value adding ones.

The same is true of the manufacturing in the North that people so decry the disappearance of. The game is all about adding value and if it turns out that staffing an old folks home adds more that humans value than does making thing to drop on your foot then we're richer for the change in what people do.

Jones, as well as a number of other people, really need to understand changes relative to the positions of others are not the same thing at all as changes in absolute levels. Whatever the relative changes between north and south over the past century (and 150 years ago everyone worried about the poverty of the non-industrial south, Somerset and Dorset being regarded as some of the most impoverished areas of the country) we are all, collectively and individually, richer than if we still had those great satanic mills working away.