Nonsense. He doesn't stand to gain anything by interacting directly with the car company which if he has a lawyer they most certainly pointed this out.
Jesus Christ. Get out of lawyer land for a second and realize if there is a flaw in the design that resulted in this outcome, you've gotta do a full teardown to find it.
If you want a neutral third party to do it fine, but they'll still need to interface with the people who made the damn thing.
The first step in any legal fight would be to root cause it to determine liability.
Arguably the best people to figure that out are those intimately familiar with the design of the vehicle - like those who designed and built it in the first place.
And true there some pressure to "sweep it under the rug" - but that's what government safety agencies are for. And they'll probably ask the designers to help figure out what happened anyway, but they (should) have the power to counter that pressure and provide oversight. I suspect the first step of any retained lawyer would be to report it to that exact agency.
This wouldn't end up being some personal lawsuit about an issue where "Don't speak to your opponent at all" is often good advice, as the courts are simply not equipped to make a ruling on such a thing. This isn't some disagreement on some contract interpretation, but a material statement of "Is this design unsafe according to the law". So those agencies that define that will need to be involved anyway, and end up taking point on any legal process too, and the process would likely look very different to "Making your personal argument in front of a jury" that some people seem to think is the end result of any such process.
Most countries have mandated reporting of safety issues already for exactly this purpose, and again they should have the teeth to enact heavy penalties if their rules are found to have been circumvented. They would look extremely poorly on any attempt by the company to strongarm the one who reported a safety issue into dropping it.
You definitely do not want the counterparty to have unfettered access to the vehicle until it has been independently inspected. They obviously have good reasons to want access but if your goal is a damage claim you should be very careful with preserving the evidence.
I'm still saying that treating this like a lawsuit isn't really correct, as "Is this design inherently" unsafe isn't a legal issue, so not answerable by the courts.
And honestly if a car company is willing to subvert a safety investigation to that extent, it doesn't really matter if you gave them "unfettered" access or not. If they're willing to break DVSA rules they'll have plenty of chances to do so during their investigation anyway.
Ok so in a situation where you're looking at a lawsuit that could clock in at an order of magnitude more than the cost of the car your plan is to let the people you're thinking about suing have access to the car before you've had an independent 3rd party perform a thorough examination? Good luck with that.