A machete attacker has been found guilty of wounding with intent after leaving a police officer with skull fractures and deep gashes to the head.
PC Stuart Outten, 28, also suffered broken fingers in the attack by handyman Muhammad Rodwan in Leyton, east London, last August.
Rodwan was found guilty of wounding with intent following a trial at the Old Bailey, but cleared of attempted murder and possession of an offensive weapon. He will be sentenced on Friday.
Metropolitan Police Federation chairman Ken Marsh said he was "saddened" by the verdict, and that what happened "was an attempted murder".
Had PC Outten not used his Taser, Mr Marsh said he "would have received further blows" and it "would have been fatal".
Jonathan Rees QC, prosecuting, said Rodwan, 56, launched the "savage" attack with a 2ft blade after being warned he was under arrest.
Rodwan claimed he was acting in self-defence and had the machete in his van for gardening work, telling officers: "My life is worth more than his life."
Rodwan has convictions going back to when he was 18.
In 1982, he was given a three-year sentence for rape, while in 1997 he received a nine-year term for two counts of wounding with intent after an attack on two people with a machete.
In a victim impact statement read out in court, PC Outten said that one cut to the side of his head caught an artery and chipped his skull.
Another cut lacerated a nerve which resulted in temporary paralysis to part of his face.
He needed operations to repair his hands and could not drive for three months.
PC Outten told Sky News he thought he would die in the attack.
Bleeding from deep head wounds, he fired his Taser stun gun but it did not work and as he fell to the ground, Rodwan ran at him.
PC Outten said: "The first shot hadn't worked, he showed no reaction and I thought 'oh dear', or words like that.
"I may have been able to fight him off, but with the blood loss I'd already gone through that would have carried on, I don't think I would have been able to stop him without my Taser.
"I fully believe he would have carried on chopping and hacking at me. My thought process was 'I need to stop him or he will kill me'".
Lying on his back, with his attacker poised to strike again, PC Outten fired a second Taser shot and Rodwan fell to the ground beside him.
"I thought I've got one last shot and if that doesn't work he's going to end up killing me."
The confrontation began when PC Outten and a colleague pulled Rodwan over because they suspected his van had no insurance.
Video footage shown to jurors showed Rodwan being aggressive and trying to drive off as the officers spoke to him.
Rodwan punched PC Outten, who then tried to arrest him.
As the officer struggled to drag Rodwan from his van, he felt blows raining down on his head.
PC Outten said: "By that time the adrenaline of having a scuffle with someone had kicked in, so I was aware that something big, heavy and sharp was hitting me on the side of the head.
"It's hard to explain - you don't know you've been cut until I realised it was blood.
"Then I put two and two together and thought he must be hitting me with a machete and realised I was bleeding heavily.
"I didn't have time to be afraid, I just knew I had to back away and stop him or he will kill me."
PC Outten's body-worn camera captured Rodwan leaping from the van towards him with the machete raised in his right hand, just before the first Taser shot.
With Rodwan lying incapacitated by the second shot, the footage shows PC Outten on his hands and knees, bleeding profusely from six deep head wounds and other injuries. He also suffered multiple skull fractures.
Yet the officer was still able to ask passers-by for his dropped radio and he called colleagues for help.
Five months on, PC Outten, the son of a police officer, has made a remarkable recovery and doctors have told him he is fit to return to work.
He said of his attacker: "I've got no ill feelings towards him. He did what he did and I acted in my role to save my own life. I don't believe he was attacking me personally, he was attacking a police officer in uniform. There is no hatred, there's no time for that.
"He'll get what he deserves, but I can't go around holding grudges because they will weigh on me and bring me down and change the way I am as a person."