Initially Toyota Online, and then Toyota UK. The details of my complaint to Toyota UK is in this thread:
There seems to be some debate as to whether UK buyers of the manual have been sold short with regard to parking sensors. I’m pretty sure at point of order the spec did include them, and going by the UK spec test cars there appears to be no sensors. Has anyone got a screen shot or proof that at...
www.gr-zoo.com
The sensors only provide audio feedback, and they don't communicate with the original reversing camera. With the way the sensors function, I'd say their presence is "meh". I am still working how what sound corresponds to what distance. But I use the audio feedback as a backup when reversing onto my driveway.