Legally in UK, you cannot portray yourself to be a medical doctor unless you have completed a medical degree and are a member of the GMC. Even if you have done a PHD in any subject you cannot call yourseld a doctor of medicine, i.e not DR. If you have a PHD you could use the title DR after your name, but it would need to be clear that you were not portraying yourself to be a medical doctor.

Physiotherapist is a protected title. It also represents what we do, and you should be proud of that and not aspire to use the title of a different profession. there is no reason why a physiotherapist should wish to be called DR. and if you do then you should consider retraining to be a DR.