In short, either we have an ageing population with more care needs and triple-locked pensions to be paid for by a diminishing workforce, or we allow immigration. Call the latter a pyramid scheme if you want, but it's how the cities have grown - from the industrial revolution drawing people to the North, to mechanisation killing rural jobs. My grandfather and his brother "left the land" and migrated to the North - and started a building firm (so provided more infrastructure than they used).
And I've cited umpteen times that immigration often means wealth-building innovation. Just in this region: Beyer-Peacock, Renold Chains, ICI, Ferranti. Even in retail: M&S, and where would Macclesfield be without Arighi-Bianci?
Examining the relationship between population ageing, economic dependency and international migration in the UK.
www.ons.gov.uk