Not answering your question but however..
Living on the edge of Birmingham as I do, with areas that are almost 100% Asian, then stopping people on the street is not a very efficient way of finding illegal immigrants. Likely to cause unrest in the area as well.
Far better to target either ethnic shops or restaurants where people are likely to work, or target places where "low paid" workers are likely to work (meat production, sandwich production, fruit picking that sort of thing).
But then you read this article, which says people employing illegal immigrants have been fined a total of £80 million, yet we have only collected around £25 million.
http://www.bbc.co.uk/news/uk-23535938
I really do think this country is totally useless at doing some things.
What is the point of dragging people through court and fining them if you are not going to make much effort to collect the fines.
No wonder this country is full of illegal immigrants, fake asylum seekers, and thousands fiddling the benefit system.
We just cant organize anything to stop things like that.