I'm having the same problem. If the BBC site doesn't see that I'm using v45 is there a tweak that can be done to show that I have v45?
Similar to using older versions of Flash and changing the version number?
You can use an agent switcher but it's unlikely going to work as I believe their would be some DRM involved in watching video from the BBC. Unfortunately for web videos if it's not on youtube it's more and more looking like you will have to abandon ship and go with a PC or Intel Mac to keep up with today's web sites for online video.