"Now that the net immigration figures are plummeting" ...

We need to be a bit careful here. We have the number of immigrants, the immigration rate (1st differential) and the change in the immigration rate (2nd differential). As I read the figures it is the second differential which is unusually high, but it is the number of immigrants that those who do object tend to object to.

I remember Mrs T once heralding an achievement because of a change in the third differential of whatever it was.