I watched a documentary on the UK Border Gang (sorry can't remember what their proper title is and it'll have changed by the time I find out). They seemed bright, motivated individuals for the most part, but as usual they appear hamstrung by daft rules.
When they detain an individual here illegally, if they can't find a passport or similar document, they can't deport them. Instead they give them a piece of paper with a stern instruction to report regularly. Then they are let go and (mostly it seems) never heard from again.
What a ridiculous waste of time and (our) money.