In uk.legal Roland Perry wrote:
I've never known that.
You don't get past the check in desk without a passport and ticket in
any airport I've been in this last 15 years

The only exceptions I've found are some American airlines who want to
ask passengers their security questions "did you pack this bag..." and
so on, as they join the check-in queue rather than when they get to the
desk. In those cases you have to wait nearby while they check in, but
can still be with them most of the time until they join the passport
control queue.

I recently accompanied a friend to an airport and she was asked by
an airline persoa (Continental) whenn when she arrived in the UK. None
of their business. A pity it was not a different friend of mine as he would
have told them to **** off since he has both UK and US passportd.

Axel