Car accidents: how can I prove that the other driver was negligent?

From Lawpack's Trip & Slip. 

In law, there are no absolute rules on who's right and wrong when it comes to road traffic accidents; for example, just because the driver was behind you when you were involved in a shunt accident doesn't mean that he or she is automatically to blame. The court will consider each case on its own merits, but it usually will take into account the following factors:

1. Was there a breach of the Highway Code?
   The courts can use the Highway Code to assess whether a motorist's standard of driving falls below the standard of care expected of road users. You should bring to the court's attention any breach of the Code if it contributed to or caused an accident.
   
   
2. Does the other driver have a conviction for a driving offence?
   If the other party has been convicted of an offence in connection with the accident, such as 'dangerous driving' or 'careless or inconsiderate driving', you can use this conviction to prove negligent driving in a civil case. You will need to write to the court where the person was convicted (either a Magistrates' or Crown Court) asking for a 'certificate of conviction' for use in civil proceedings. The practice varies from court to court, so do ring them to find out to whom the letter should be addressed. The court will also be able to tell you how much you will have to pay in fees. The other party may defend this claim by stating that (i) he was not convicted as alleged; (ii) he was wrongly convicted; and (iii) although he was convicted, the conviction isn't relevant to your accident.
   
   
3. Did mechanical faults exist?
   If the driver knew or should have known that his or her vehicle had a mechanical fault which caused or contributed to the accident, he or she may, depending on the exact circumstances, be liable due to negligence.
   
   
4. Were seatbelts worn?
   If you didn't wear a seatbelt or headgear at the time of the accident, you may be contributorily negligent (i.e. the other party may be able to prove that if you had worn a seatbelt, you would have reduced your injuries or avoided them altogether). Your damages will be reduced by a percentage reflecting the extent to which the court finds that you contributed to your injuries.