What do UK bouncers look for when IDing someone?

I have A lot of experience working in bars and clubs so in my opinion look out for anyone looking nervous like his/her friends are making them try when they know they got no chance, then I.D his/her friends too just to be safe. Also there is the complete opposite, girls/boys being over confidant, like they have a god given right to be there, but plz don't mistake this for ur average drunker behaviour because if you I.D someone who is clearly of age but just drunk this can coarse a negative Reaction unnecessarily. But as the bouncer it's ur way or the high way weather they like it or not it's better to check then have a fine for letting in an underage child.