To what extent can a defendant in the UK see the evidence agaist him/her to allow him/her to prepare a defense?

I'm asking on behalf of a random person I encountered who was involved in a car accident, and who may have disclosed incriminating evidence against him/her while in a semi conscious state. This person does have a legitamite defense but may have fudged his/her statement considering the state that he/she was in at the time.