Thanks for your responses.
Eventually got to the bottom of it
Having replaced the rear flexi hoses, I was getting help with bleeding the brakes. I asked for the brake pedal to be released after locking off the bleed nipple and noticed the brake lights were still on. The wheels were refitted and a test drive confirmed that when the pedal was lifted the binding stopped
Found the pedal spring was rusty and not allowing the it return fully!
Not sure why it was just causing the right rear to bind, but anyway all fixed now