Minor traffic accident

[smc987]

I recently reversed into a car behind me, the driver got out and we both inspected his vehicle, the only visible damage was a circular mark on his number plate from my towbar and he seemed happy no damage was done. we did not exchange details although i think he took my number. we both then drove off. Should we have exchanged details and could he now come back saying more damage was done??? there were no witnesses, should i inform the police