The questions are getting more intrusive because the state has let it get to the point now that a tenant who decides not to pay the rent will take over a year to get out (legally).
So, landlords only really have any power to exercise BEFORE a tenancy commences. Given that, landlords are now requiring much more by way of information about who they are about to hand that expensive asset over to.
I would no let to anyone now without:
-Copy of passport/national ID card
-Work reference
-3 months Bank statements if work reference doesn't show how much they earn
-Previous landlord's references (to be verified, not taken at face value!!)
-2 months deposit + month in advance rent
It's just too dodgy now to be letting anyone in to your place.