The star of Saturday night TV was arrested at 4pm on Sunday after a three-car smash.
Witnesses said the 42-year-old TV presenter looked dazed after hitting two cars in his Mini in South West London. One added: “Ant looked like his world had just ended.”
Ant got “agitated and argumentative” with a policewoman as she arrested him on suspicion of drink-driving.
Witness Jake Spencer said the Saturday Night Takeaway presenter rowed with officers as they tried to put him in a police car after he failed a breath test at the crash scene.
He added: “Ant looked in a right state and was acting argumentatively toward a policewoman.
“I couldn’t believe it when I saw who it was.
“The woman was trying to arrest him and get him in the police car but he clearly wasn’t having it.
“He was not making it easy for her and he seemed to be trying to wriggle out of her clutches. He was not in a good way.
“Eventually she got him in the police car. There were about six or seven police cars in total.”
Ant, 42, who booked himself into rehab in the summer for drink and prescription drug addictions, was being questioned at a police station.
He allegedly hit two cars in his black Mini sports car at around 4pm as he and mum Christine headed home after walking their dogs.
It was thought Ant's car had veered into the wrong lane after coming round a sharp bend on Lower Richmond Road, South West London, and hit a green Mini — then crashed into a BMW X5.
Less than 24 hours earlier, he had been performing with telly partner Declan Donnelly on ITV's Takeaway show.
Motorcyclist Nicholas McNicol said: “I came on the scene moments after it happened and he was being escorted to the police car to be put in the back.
“Everyone was in a state of shock at who it was.
“I was driving past very slowly and Ant looked straight at me and I thought he looked tired. I was only about 3ft from him.
“His eyes looked very heavy and he had a solemn face — it looked like his world had just ended.
“He was the only one being put in a police car. One of the Minis had obviously come straight across the road because it was facing the wrong way.”
A third witness, who lives nearby, said: “I was at home when I heard a huge bang outside which was so loud I thought it was a train crash.
“There’s a level crossing nearby and I genuinely thought a train had wiped out a car.
“I went to if anyone needed help. As soon as I opened my front door I heard the horn of a car blaring non-stop and ran towards the sound.
“Near a bend in the road there were two badly damaged Minis which looked as though they’d collided and a BMW X5 — and people wandering around in shock.
“A family had been in the green Mini which had its front end completely smashed in.
“A little girl aged six or seven was crying as her mum tried to calm her down.
“She looked really shaken up but didn’t look seriously hurt. Then I saw the driver of the black Mini, a flash one with red sports stripes and alloy wheels, and recognised the driver as Ant.
“He looked really, really traumatised and unsteady on his feet, which I put down to shock because his car was a wreck. It must have been a big impact because all of the airbags had gone off inside Ant’s Mini. He looked awful.
“He was wearing a black jacket and wellies.
“He looked as though he’d been walking his dog because he was walking around the wreckage holding a lead. There was a woman in the car with him, who I presumed to be his mum, plus two dogs.
“None of them looked to be seriously hurt. They were just in shock. I think an Asian family were involved and passers-by were helping them before the ambulance and police arrived.”
A video of Ant’s arrest shows him appearing agitated as officers put him in their car.
He appears to move around in the back of the car until an officer opens the back door of the vehicle to speak to him.