I did my Class 1 about two weeks ago and got the all important piece of paper in the post yesterday. Wear whatever you are comfortable in. I went in jeans and trainers and at no point did I feel the docs and nurses were being unprofessional. Besides, white trainers go rather well with the dressing gowns
If I could do the exam again, which I will in a year, I would be a bit more careful when driving in before the exam. I found that two hours in a car with loads of wind noise did my hearing no good at all. Only just scraped through the hearing test. Prehaps an ear plug in my right ear would have made things easier.
Simon