Lottie
The process by which this works is contained in Land Registry Public Guide Number 19 here: -
http://www1.landregis.../public_guide_019.pdf
Read from paragraph 7 onwards. I fear that you are going to have to invest in a surveyor to have this drawn up for you. Only with that plan will the land registry to able to register your Title with 'Exact Boundaries', not what they refer to as 'General Boundaries'.
Its the only way if there are not fixed features (like immovable ditches, trees and walls that mark the boundary. The surveyor will draw a plan based upon the fixed features that do exist around the area that is disputed by your neighbour.
I have no idea how much it costs to draw this thing up.