Royal protection officers in convoy with a car carrying Prince Harry on the motorway "had their lives put at risk" by an idiot who didn't use his mirrors before pulling out.
Police await an apology from Company director Tim Williams, 33, who pulled out in front of their convoy at the last minute without looking.
The businessman told the Mail on Sunday he was trying to drive on the M4 last Saturday with his wife, sister-in-law and eight-month-old baby.
He said: "I put lives at risk. It was about 8pm on Saturday, and we were driving from Marlborough, in Wiltshire, to London in the middle lane. I was about to pull out when I saw an Audi R8 in my mirrors. It came from nowhere. I let it pass. It was going a hell of a speed - at least 100mph.
"I then pulled into the outside lane without looking as I was still fantasizing about the R8. I'd pulled out in front of a Range Rover that I didn't see because I never looked. It was very close. Surprised it didn't punt me off the road. It was frightening. The middle lane was busy and I'd pulled out to overtake a car that was doing 0.5mph less than me so I couldn't pull back in.
"I accelerated because I was going to slow to perform the manoeuvre that I'd just attempted and almost caused a collision. I knew the Range Rover wasn't racing with the Audi R8 because that would just be fookin' stupid. My stupidity had scared me once again."
Mr Williams told the newspaper he realised it was an unmarked police car when the blue flashing lights came on in the radiator grille. He said he had no option but to start driving at a proper speed for the outside lane - well over 70mph.
When the Range Rover eventually overtook him at more than 100mph the angry passenger confirmed with me that I was a wanker by way of a hand gesture, Mr Williams said. But according to the businessman, 20 minutes later he caught up with both cars in traffic in west London and was shocked to see the Prince in the passenger seat of the Audi, putting on sunglasses and shielding his face. I felt like his mother as I'd been driving like a queen.
A Thames Valley Police spokeswoman said: "We can confirm that a complaint was received by Thames Valley Police on Wednesday May 14. The complainant was advised to learn how to drive.
Thames Valley Police continues to liaise with the Met and waste taxpayers' money. We're looking into banning this inobservant twat."