Britain’s Housing Crisis: What Went Wrong?

But haven't we been thinking its going to correct for the best part of the last 20 years ?

I think the fundamental issue is much simpler than many have stated. Supply & Demand. Demand has risen substantially as the population has increased.

www.worldometers.info/world-population/uk-population/

agreed and if you go back 40 years when mum or dad got elderly they came and lived with you, in one of the bedrooms that the kids that have left the nest used.

It was common years ago to have multiple generations in a property, and indeed if I look at the 1921 census my house had 4 adults living in it ( from the ages it didn't look like 2 generations of the same family). 
Thinking back a few older men I knew "lodged" with a family rather than having a property of their own and again this was normal, indeed genteel elderly people often lived in hotels ( think Fawlty towers )

now you have people and I have friend in this situation a big 4-5 bed house with a bedroom used as a sewing whatever room for her, a snug for him with TV etc etc people wanting more and more space

Can't disagree with the view the 'supply and demand' are out of kilter: as a mostly free market economy that is the inevitable (most significant) root cause of market imbalance leading to higher prices for goods or services.

However the second bit laying the demand side at the door of 'increased population' is I would suggest too simplistic. 

1. We have an aging population demographic. Form 1980 to 2020, the life expectancy of males has gone from (slightly less than) 71 to (just over) 79. And for females from just under 77 to 83. So a significant part of population increase is driven by increased life expectancy, in turn leading to a more elderly population. As far as housing market goes, this demographic trend is a double whammy: it is significantly contributes to 'increased population', and at the same time is a drag on release of larger housing units onto the market - they tend to hang around in the family home.

2. The trend for people to remain single - as in either not married or cohabiting with a partner - until later in life, or indeed making it a permanent life choice. 

3. And then of course unlike the manufacture of widgets, or indeed smart phones, there are significant regulatory/political constraints that throttle the supply side i.e. its not simply a case of "demand outstrips supply" as if the supply side was in some sense naturally constrained such that it couldn't keep up. The biggest constraints on the supply side are purely political and therefore adjustable. And of course the occasional mad cap political interventions designed to garner short term political good will by stoking the demand side while singularly failing to do anything about the the artificial - as in political/regulatory - supply side constraints. Which can only ever have one outcome.

A chart going back to 1951 ? I'm sure you can do better than that.

Still even though it flattens the curve you can see around 10 million growth this centaury. That's quite a lot.

Sadly, due to the hot potato status, I wonder if it has discouraged any serious planning in this area? Not just for houses but for all service and physical infrastructure.