A hedge of any kind must be a MINIMUM of 2 metres before action can be taken under the High Hedges Act. In other words, there is nothing to stop you growing your bamboo or anything else to as high as you like if nobody objects and asks for enforcement.
Talk to your affected neighbours and ask them if they mind your bamboo growing larger. If you offer to thin it and remove canes from time to time, I would hope they wouldn't mind.