Firsty was there any damage caused to anything other than the car? If the post is not damaged then there is no need to report the accident and no offence to leave.
Secondly If there was damage to the post you have a duty to reported it to the poilce as soon as paracticable or at least within 24 hours.
Officers will want to speak to you regarding the circumstances and unless there is any evidence of driving without due care or careless driving and it is just a simple accident and the insurance is willing to pay or you personally then that should be the end of it.
You wil be reported for the offences or failing to stop and failing to report an accident and the facts will be submitted to a central summons unit where a decision will be made as to whether to prosicute or not. There is a time limit of 6 months to progress the report so it could be some time before this is finalised
A rough guide to possible outcomes if it goes to court are.
Momentary lapse of concentration or misjudgement at
low speed
Band A fine, Band A fine
3 – 4 points
Loss of control due to speed, mishandling or
insufficient attention to road conditions, or carelessly
turning right across on-coming traffic
Band B fine, Band B fine
5 – 6 points
Overtaking manoeuvre at speed resulting in collision of
vehicles, or driving bordering on the dangerous
Band C fine, Band C fine
Consider disqualification OR
7 – 9 points