Once again, it's ancestry not foreign born, and London had it in waves, constantly, whereas the other cities had the one big wave in the 1850s famine.
The second figure 1851 pertains to that bulge (and btw London still took more than the other cities in sheer numbers then) - the rest of the waves London continued to take the majority for 180 years more (not to mention before):
For Britain as a whole, 1 in 10 had at least one Irish grandparent in 2001 and 1/4 claimed ancestry. It's not a stretch that the main recipient destination by far, for centuries, would end up with a third.