I don't do this often, but...

Perhaps the issue is not that the population is shrinking, but that the economic system works under the unrealistic assumption of a forever-growing population in an already overpopulated archipelago? Would a shrinking workforce be still an issue if its labour was used to fund their pensions in the old age, and if industrialisation and automation reduced the need of such a workforce, instead of both things being mostly used to further the concentration of capital under the few wings of a bunch of global vultures?

Nah, I must be insane. I'm supposed to assume that "import immigrants" is the holy solution. Except that this "solution" clearly won't work for every single population in the world.