I can't see how locking up someone who has legal status can be legal, in the absence of evidence that they are illegal. The fact that they have not produced that evidence is not evidence of illegality

Again, there can be no evidence of illegality, only absence of legality evidence, and it clearly is legal to detain such people.

The fault lies with successive governments who failed to provide the Windrush folk with evidence, or to even recognise that there was an issue.

Kate Hoey said on Peston that they had targets for removing illegals under Jack Straw, and I am sure there has been ever since.