Labour estimates that these changes will lower the number of visas granted annually by around 20000. That is presented, in their documents, as a reduction in annual net migration of around that amount. But that is true only in a transition, immediately after the changes are introduced. The stock of people here on such student and related visas will fall, but after the initial transitional period there will be little or no expected change in the net inflow over time (which is as one would expect, since the residence approvals target is the key consideration there).