As a country becomes poorer, locally made goods and services stay the same price - because local wages reflect the lower wealth of the country.
But imports and travel outside the UK become much less affordable. And we import a lot.
In 2000, the UK's GDP per person was about 20% below the US, 20% above France and Germany and 50% above Australia.
It's now 30% below the US, 5% below Germany, 20% below Australia. Pretty shocking. We're still 20% above France (France has very similar structural financial problems to us). Oh, and don't blame Brexit for the drop compared to Germany - we've grown faster than them since then, the drop was before that.
If you want to imagine what it will be like for the UK in another 25 years - when your boys are whatever age they will be then - as this decline continues, think about how it is for people in Croatia and Portugal, or Poland 15 years ago. That's about the same amount of economic decline again.
I mean, it's not disastrous - but people have far less, and young people very often leave the country for better opportunities abroad. If you think we're currently in a COL crisis, that's the very start of this change.
If it becomes a spiral, the exit from London continues and London becomes a normal capital (rather than one of the great world capitals, with the huge inflows that come from that), then the impact becomes even stronger.
I don't want that. I'd like the UK to continue to be a good place for all our children and grandchildren to live.