If it helps jog your memory, if your convenient friend happens to be what many seem to refer to as an "international driver" - which in actual English translates to foreigner, or otherwise not resident in the UK, and you name them as the driver, the police will immediately ask you to prove that they were insured (knowing that foreign insurance will not cover them, and knowing strongly suspecting that the friend either wasn't driving or wasn't even there).
I note that whilst your post was not a witness statement sworn to be the truth, the whole truth and nothing but the truth, you make no mention of asking your friend if he recalls the incident, merely that he has "gone back to home". Most people would find it curious that you appear to be seeking legal advice before making any attempt to get your heads together with your convenient friend to try to work out who was driving.
I also note that you make no mention of making any attempt otherwise to determine who was driving, instead preferring to set out your excuse that the incident was so long ago and that your friend has "gone back to home".
The law requires you to name the driver. If you are unable to do so, you arew required to provide any information that is in your power to give that might lead to the identification of the driver and it then becomes part of a defence if you are able to persuade a bench of magistrates, on the balance of probabilities, that you both do not know who was driving and cannot with reasonable diligence work out who was driving.