I believe you will have to do a Physiotherapy course at a recognised institution before you can call yourself a Sports Physiotherapist. Physiotherapist and Chartered Physiotherapist are protected titles which means you can't call yourself a Sports Physiotherapist unless you have qualified on a recognised course (all of which are degree courses and as you say you should be able to enrol on an accelerated course with your Sports Science degree). You can find out more by going to the Chartered Society of Physiotherapy website at http://www.csp.org.uk. If you are only interested in the sport aspect of Physiotherapy then maybe you would be better going down the other route in which case presumably you could call yourself a Sports Therapist or Rehabilitator but not Physiotherapist. Hope this helps!