Thanks to those who provided level-headed replies (and no thanks to the mean-spirited replies).
To answer my second question - Tesla do have a process for requesting an investigation/diagnosis. You need to raise a service request via the app (I used the "Other / Something else" category), and say you want a diagnosis. They will contact you for further information, and you will need to provide as much detail as possible after that, e.g. emailing videos to the email address they provide. They keep the logs for 3 weeks by default, so you need to do so within that timeframe.
In my case I raised the request on 20 Apr, they escalated to their Engineering team on 28 Apr with an SLA of 5 working days, and on 6 May they responded. They confirmed that it was on autopark at the time of the accident. However, they could see "no explanation" for the accident, could see "no sign of an underlying fault", and pointed to the Terms & Conditions which state "Autopark may not steer Model 3 appropriately. Pay attention when parking Model 3 and stay prepared to immediately take control." In other words, it is normal behaviour for the software to periodically crash your car.
I pointed out that it wasn't a reasonable expectation for a driver to be able to take control in the time frame available. If your car unexpectedly starts moving at a speed of 1.5meters per second towards a neighbouring car which is 15cm away, then you just have 0.1s to stop it, which is not a realistic amount of time for humans. They responded by repeating the Terms & Conditions.
I asked about whether using autopark again is likely to crash the car. They said they didn't know, but their recommendation was to try autopilot on the motorway first and if that doesn't "behave unusually" then perhaps try autopark again. I said that a motorway wasn't perhaps the safest place to experiment with such things, but they said I could try any road that had clear markings, although did remind me that if it wasn't a dual carriageway or motorway then I shouldn't really be using autopilot. The conversation didn't appear to be going anywhere productive by this time so I ended it.
Personally I don't think they will be able to hide behind the Terms & Conditions indefinitely. There's a clear parallel with Boeing's Maneuvering Characteristics Augmentation System, and even some parallels with ICL/Fujitsu's Horizon, plus Terms and Conditions are not enforceable if they are classed as unfair or unreasonable in a court of law.
Incidentally, I did ask the insurance company if this could be classed as a "no fault claim". They responded that it is possible for the liability to be placed on a manufacturer due to a manufacturer fault, but the manufacturer needs to confirm this. Unfortunately Tesla said that there was no fault.
Repair bill for my car is just over £3.5K, and the other car is just over £1.5K. Not to mention the £6K I spent to purchase this feature.