Just to say i had some troble with my bank they did call me uninitiated, they did ask me some security questions d.o.b, and then asked me to for random letters of my security q. At no point did they ask me for my National Insurance number. I was sort of expecting the call as i owed them alot of money so i knew it was them. But they did use foreign call centre which a had a really weird number.
Im not trying to confuse the matter jus wanted to giv my experience, and only second or even third the advice every1 else is given. Never give details out over the phone, if it is the bank you should have a security word for which they will ask to name two letters from. They will never ask you for the whole word so be suspicious of any call tht does.
Badfish