If your vehicle is not owned by a business, but you use it to carry out business activities, then you are able to claim a portion of its costs (repairs, WOF, Registration, petrol, insurance etc).
You can either keep a log book of all the trips and kilometres you do, recording whether each trip is personal or for business (note, home to work is not business), or you could record the kilometres for work trips only.
Keeping a log book is preferable as you only need to do this for three months and there is no limit on the kilometres you can claim. Recording business trips only is easier, but you can only claim a maximum of 5,000 kms per year.