No, it's not OK to take essential oils internally in Australia for therapeutic purposes, unless prescribed by someone with TGA approval, and there aren't many of them, because an aromatherapy qualification does not give you TGA approval. If someone wants to self administer there is nothing anyone can do about it, and the same applies in the UK, it's just that hardly any qualified professionals involved with aromatherapy would be qualified enough to do it.
It is being promoted in Australia by the Young Living MLM brand which comes from USA where there is no regulation, and it is also gaining ground in the UK thanks to Young Living, multi-level marketing doesn't usually attract qualified therapists, it is usually just people pushing the marketing materials eg 'a warming sensation after using neat oregano essential oil is a sign of toxins being released', sounds much more friendly than 'oregano essential oils is a known skin irritant, a warming sensation is to be expected'.