Are you purchasing this through the Sheriff or directly through the bank ? Either case, there are a few pitfalls, unless you have done your proper homework and its dirt cheap, stay away.
Check outstanding rates, water and electricity. These can run into thousands at times. There will be some clauses of occupational rent as a percentage of the purchase price, which you have to pay from sale. You will also be responsible for clearance and other certificates before transfer is done. These things can take time to sort out depending on the issues. The conveyances (which you cannot choose), sheriff and banks also generally drag their feet to get the transfer done which is in their interest as they make more money of you through the monthly occupational rent. You generally entitled to live in the home from the date of sale, depending on the contract, but generally cannot make any alterations etc until transfer is gone through. Transfer on normal properties takes a few weeks with the deeds office, but in a case of repossessed property it can take many months.
If they do have the keys (sometimes they don't as the defaulter may have absconded without providing them), get a locksmith and take occupation as you entitled to it