Use sub-titles

What annoys me, really annoys me is the discriminate use of sub-titles on TV when people are being interviewed.

There should be a clear rule, a mandatory rule of when someone can not be clearly understood, then use sub-titles. If they are Aboriginal, Pacific Islander, PNG, Middle East then sub-titles seem to always be used even if there is reasonable clarity. However they don't seem to get used when people are from Britain (inc. Wales, Scotland), SE Asia, China, India ... when often there is no clarity. There should be no offence to the person being interviewed. If the interview is in English then the communication (to us) should be in English. If sub-titles will help, then use them.