A couple of times I've been at the First passport/BP check, just behind a family of 3 or in one case 4. The Agent looks a bit embarrassed and says - only two can come through. I stepped fwd and offer to guest the other pax - everybody happy. With the chap who had two daughters (about 12-16) I stepped fwd at the same time as another lone traveller stepped fwd too - we all went through, with a nice Thank You from the dad.
No harm done as the two teenagers weren't going to drink my champagne!
