It doesn't really apply at all in some ways, you can decide yourself to pay nothing more than the interest amount each month but it would be better if the bank agreed to it. The arrears don't really matter and are probably in your favour as the bank is more inclined to agree to interest only if it is obvious you cannot pay the full amount as presumably you can't or you wouldn't be in arrears. Ask them for interest only, if they don't agree then you must decide if you are going to make the decision for them, just deciding to do it yourself does not change it on their systems to that status.