You need to advise your insurance company, the claim for damages will be against the insurance company of the person who hit you from behind. I expect your works car insurance will have legal cover - this is what happened when I suffered whiplash, my insurance company appointed solicitors to handle the personal injury claim for me (and they paid for it). You will need to provide medical reports etc to substantiate the claim, but you need not worry about that at this stage - the most important part is to register the fact that you want your employers to include a claim for personal injury to yourself in the claim against the third party. If you don't get paid when you are off sick, loss of earnings can be included. Don't appoint your own solicitors - let the insurance company do that, they will know who they use for PI claims.