Hello All!
My understanding is that your entire thesis (and proposal) must be original. In the UK system, you are not allowed to re-used work that has been graded and given credit. You may certainly cite yourself, but do not re-use anything that has been graded and given credit.
Others might continue to expand on this. I would just encourage you to be original in your thinking. It has evolved since previous modules I am sure! Your own previous work is certainly worthy of citation if you wish.
Lee