The UK has a backlog of almost 4000 people who it deported, or threatened to deport, because they can't prove that their parents had a right to bring them to the UK as citizens before 1973.

This is referred to as the "Windrush scandal" in reference to the Jamaicans who were invited to move to the UK to work, starting in 1948 on the HMT Windrush.

The UK government's attitude from the beginning has been, "We will deport you unless you prove we can't." This despite having deleted the database that many of them would have needed to cite in order to prove that.

After mistreating people so much, the UK has an obligation to take a forgiving attitude: if a person's case seems valid to the extent it can be checked, say yes.