According to the Telegraph :
Police groups have refused to accept Andrew Mitchell’s second apology over foul-mouthed tirade at armed officers, as David Cameron faces calls for an inquiry.
The Conservatives have been hoping the second apology would “draw a line” under the incident but this morning the furore showed signs of escalating.
Andrew Mitchell: Police refuse second apology as calls for inquiry grow
And according to the Sun :
The officer, who wrote his report for his superiors only hours after the incident, said he did so because Mr Mitchell told him: “You haven’t heard the last of this.”
The PC explained: “I write this for your information as Mr Mitchell’s last comments would appear to indicate he is unhappy with my actions.”
Official police report shows Andrew Mitchell called PCs ‘plebs’
So apart from the swearing and the insults, I suspect that Andrew Mitchell probably now also regrets saying “You haven’t heard the last of this”