I went for an assessment at a nhs run driving assessment centre (there are several dotted around the country, mine was incorporated with a small hospital). I went there myself so did not have an actual referral, because I could feel that I was struggling to control manual car, as legs were not great.
they were very helpful, asked lots of questions, did normal vision tests et , then lots of physical responses etc. lifting legs, feet, arms, twisting etc, which all seemed perfectly reasonable assume you need to do all these when driving a car.
the result was that I needed a new automatic car, with hand control adjustments, which we got sorted. I am safe now, and it feel better driving my kids about etc. I am still independent and that means so much more than having to have an adapted car.
i think the costs of the assessment was free, you get a big report with findings and recommendations, all of which I took on board, and I passed a copy to DVLA. It was recommended that I have a few lessons (more familiarisation than lesson, to get used too using adaptions), which did cost.
If you qualify for motability scheme (currently high rate DLA, not sure about PIP), and get your car through them then most adaptions can be sorted, you would need to speak to them. Otherwise cost of adaptions I think in region of £800 (guess it depends what’s needed) but you need automatic transmission often, so may need to replace car.
Feels like a lot of fuss, but i took the attitude that I’d rather be safe and legal, as didn’t want to harm kids, other road users etc. apart from a lot of paperwork to DVLA etc all parties seemed satisfied provided you were a safe driver. Tell insurance company also, although think they’re happy if DVLA happy.