I owned and let out two apartments in the UK and I can assure you that the tenant had to provide me with:

Bank references (that they were good to pay the monthly rental)
References from previous Landlords (if any)
and, if I asked, confirmation that they paid their utility bills on time.

They would NOT have been permitted, under the Agreement, to even BREATH without my permission (;D) let alone sublet to someone I had no knowledge of. Quite illegal.

Similarly, if you take out a mortgage to buy a property to live in for yourself you have to have permission to let it out by the Bank or whoever provided the mortgage since it isn't YOURS to let out to an unknown person until you own it outright.