In short, you do not have a legal right over it. It does not come under data protection as it is overpowered by The Police and Magistrates Act.
However, at the same time I forsee no reason why you can not have a copy. I imagine, it is force policy to oblige or not as paul states.
The offices are now called "Crash Clerks" as the word was accident was dropped due to their always being something or somebody to aportion blame.
However, to be honest I see no reason why you need your statement. The only purpose of a statement is for the courts. If you were called as a witness, it is only at the discretion of the court whether you can use your statement anyway. It is little more than an aide memoire, and must NEVER be read verbatin in the dock. The bone fide facts (real evidence) should come from your mouth not a piece of paper whilst testifying.