Hi Graeme,
There is potbound and there is POTBOUND. *You can usually pop the tree out of the pot and check out the roots to see which is the case. *Some adventurous roots trying to escape the pot is not usually a problem. *You can clip them away to keep the drainage holes clear and wait for dormancy.
You know your plant is rootbound when:[*]the soil is not draining well and you have difficulty keeping the soil evenly watered[*]the plant is suffering in some way[*]when you examine the roots you see several spirals of roots encircling the container or notice the plant edging up out of the pot like a cobra ready to strike
Then you need to take some emergency action. *You can find some more information
here, and the details on emergency repotting are in the second section.