I saw something on the news about this earlier, its down to a number of people who entered the UK on student and short term visas in 2021 following the “previous policy changes” mentioned here that only gave them a right to stay here 3 years. The “expert” on the news I saw said they have been waiting for years with the anticipation this will happen once those visas expire and people have to leave.

All that money from pushing most employed workers salaries down to as close to minimum wage as they can get away with has to end up somewhere.