That's not the actual scenario Peter, the UK birth rate has risen by 18% in the last 10 years (according to which statistics you use of course), largely due to second generation immigrants according to this
Inpendent report. It's not like that everywhere, Italy is one of the worst European countries for falling birth rate, due to all the kids deciding to stay at home for Mama's cooking.
Any country with a population the size of ours that can't provide an education system that will give it the number of skilled people it needs without relying on immigration is doing something wrong.