Hi RosiePosie
They ask things like date of birth, post code etc and then they will ask you one random question. I can't tell you what that might be - but it varies from one person to another. One of my relatives was asked to confirm his last address. (He hadn't lived there for 20 years). A friend was asked to verify which benefits she had been on. (Good thing she could remember going back 30 years!)
Some people get their identity confirmed and some receive notice that they still need to confirm and have to either go to a job centre or have a home visit - in which case they then look at three documents - including one with a photo id if they have it.
BIS
Nothing on this board constitutes legal advice - always consult a professional about specific problems 
