At best, nothing will happen to you. It may be that there is not enough evidence for you to be accused of common assault and the police just leave it at that.
If however they do find evidence of what they deem to be a common assault, then the most likely thing to happen to you will be a simple caution. At worst, I would imagine a conditional caution. To be given any type of caution, the police need to have enough evidence for a successful prosecution if it was to go to court, and you will also have to admit the offence. Cautions are out of court disposals for adults.
I highly doubt it will go to court in any case, because it is the lowest form of common assault and if the police do find evidence of a common assault then likelihood is that you will be offered a caution rather than having to go to court. It is a minor offence.
I think it will be very harsh if you are charge with this.