PP, quite possibly you're right that the author wants to add intrigue for his book, and I too found the number plate idea of his ludicrous, but the fact is that JC DID own that red car, and there was supposedly trace evidence of Suzy having been in that same car. However, I think that's all irrelevant: Mr Kipper was driving a black BMW that day, and that's the car that took Suzy away.
Another witness, a black taxi driver came forward to say that he'd collected a man who looked strikingly like the photofit of Mr Kipper from Stevenage Road (where he'd left his BMW) to Shorrolds Road, just 1.5 miles away. He said the man was holding a bottle of Champagne and pamphlet style property papers.
Mr Kipper clearly had pre-planned the abduction, hence him leaving the BMW at Stevenage Road: he intended to either try persuade or force Suzy into his car by first getting into hers. It's obvious.
The witness who lived in Shorrolds Road was the one who described Kipper's appearance, which looks remarkably like John Cannan. He looked out his window as he heard a couple arguing in the road. They possibly argued because when he'd arrived 15 minutes late - and IF Suzy had forgotten the keys - she may have told him they'd need to drive back her office to collect them, and no way did he want to chance being seen. There's also the possibility that Suzy was surprised it was John Cannan who she'd allegedly been dating, and was annoyed with him for fooling her into meeting him. It's not usual for an estate agent to argue with a prospective buyer is it?
Another witness, a van driver, said he'd been forced to swerve between the two locations when Suzy's white car was being driven fairly fast and haphazardly. He looked and saw the woman driver staring at him and said it looked like Suzy. She had a dark haired man in the passenger seat.
Another witness said he had gone for a run in the park just by Stevenage Road when a white car came along pressing its horn non-stop. He too said the woman stared at him with a scared look on her face, and had the same man next to her. It's also strange that Suzy parked her car haphazardly without applying the handbrake or locking the driver's door. She also left her purse in the door pocket. That suggests she was forced possibly by knifepoint and forced into the BMW.
Another couple did say they spotted a couple who looked like both Suzy and Mr Kipper laying on the grass in the park with a bottle of Champagne, which sounds odd, and could just be coincidence, but if they had once dated it's possible he forced her to lay there against her will and she was simply too terrified of him to try and escape. Whoever that couple were they never came forward, but they may have had no connection at all and for whatever reason didn't/couldn't come forward...
Another witness, a shopkeeper, said the same man fitting the description came into his shop early morning and asked for the most expensive bottle of Champagne. He vividly remembered him and even described his voice and demeanour.
John Cannan was known to woo women with Champagne, and it would be remarkable if this Mr Kipper also turned up to view a property holding a bottle of Champagne and fitted the exact description of Cannan too, right down to his build, height, colouring, facial features, and clothing.
John Cannan frequented the Fulham wine bars where Suzy used to go, and he was never able to account for his movements that day.
There's never been any point in Cannan admitting to Suzy's murder because the judge ordered that he must stay in prison for the maximum amount of time, so JC wouldn't have got a reduced sentence in admitting he'd killed her. Besides that, he's a psychopath and enjoys the power he has over the police and Suzy's family by refusing to tell them where she is.