My friend's flight was to Hong Kong and there had never had passport check by UKBA for this flight before. I saw UKBAS built some border-check desks before the boarding gates in some airport but did not see them used for a while. Are they operated recently? Some countries have the passport control w...

I heard this happened to my friend traveling back to China from LHR last week. He was asked to show tthe passport to UKBA staff at the boarding gate and the staff made note about it.

What does this action about?

Only for the people over-stay from the visa validity?