I am 80 years old and began driving at 16. I was a motor engineer including in both army and civilian times, and I have passed driving tests on motor bikes, tracked vehicles, heavy goods, public service vehicles, open cast machines and instructed on these vehicles too. I have been diagnosed with Parkinson's disease and the consultant has informed DVLA Swansea so, like all over 70s, I'm now limited to motor cars only for three-year spans.

I have been assessed by my doctors and consultants as OK to drive and have had a private test by an instructor and deemed to be at the correct level and standard of skills, and my car insurance has been informed and accepted my condition. My question is this: on watching TV programmes testing by police for drink/drug driving, the accused is asked to perform certain activities including balance, index finger-to-nose and walking heel-to-toe along a straight line. Parkinson's disease symptoms include balance problems but this does not interfere with driving.

What is your view on this and how do I stand legally? Are traffic police taught of such anomalies and would a police doctor understand the position were I to fail these elementary balance tests? I have never driven after consuming any alcohol.