mystery bamboo

Apologies for the repitition, I kept getting error messages when trying to update my earlier question!

Could be one of several bamboos - Semiarundinaria, Pseudosasa, Himalayacalamus, Indocalamus, and possibly Fargesia, though less likely. Suggest you google those names for details - ID is often made from the height, but in your case, you can't tell as its in a pot, but other features such as the colour and thickness of the stems or culms, colour of the sheaths, etc.
Whatever it is, it may need some protection if we have a winter like last year's, so plan to move it somewhere more sheltered if we do. I'd wait and split it next year in Spring if at all possible - if its desperately potbound, I'd compromise by putting it in a larger, deeper pot for winter, and then turn it out and split in the spring. If you split it now and pot them up, their chances of survival are lower outside in winter than if you just repot the whole thing.

Thanks Bamboo :-) I guess I'll just have to be patient which is the most difficult bit about gardening!