Warden, Neville Brown, was unconscious before he hit the ground after Rory Dain , 20, of East Lane, from Wembley used his eastern fighting techniques to stop him doing his duty.
But that has now been cut to 18 months by Judge James Paget, sitting at London's Criminal Appeal Court.
The judge told the court how, on 5 October 2003, Mr Brown had been about to slap serve a ticket on Dain's mother's car when Dain arrived and an argument began.
Dain drove the car away and then returned, attacking Mr Brown from behind with a kung fu style manoeuvre, which knocked him unconscious and led to him suffering a fractured cheekbone and other painful injuries.
'This attack resulted in serious injury to a public servant,' said Judge Paget, sitting with Mr Justice Beatson.
But, allowing the appeal, he said Dain had been doing well since being sent to jail.
The judge added that he was taking into account the fact that Dain usually acts as a full-time carer for his mother, and the impact the sentence would have on her.
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CRIMINAL COURT OF APPEAL/rg
31 January 2005