No idea Rob, but I think it could probably be done from underneath.
After 2 months, my radar is finally fixed... I dropped off the car this morning, and was done by lunchtime. Sadly I had to go to Watford Audi, the nearest service centre that had the right equipment to calibrate a new radar sensor. Watford were pretty good, but still didn't address the rattles and noises I asked them to look at, disappointing considering the 2.5 hour round trip to get there.
Whetstone Audi were next to useless. Despite my telling them it was the radar system they never mentioned that they don't even have to tools to fix it until it had been in their workshop for two days. They were then meant to book the car into Watford for me (same group), but despite chasing them repeatedly, they never ever got back to me with a booking, and I had to do it myself.
Compared with the likes Mazda & Toyota, brands that don't pretend to offer a premium level service, the service and warranty experience with Audi sucks balls. Any issue with the Japanese brands and you can have your car seen in few days at most, the issue is resolved, and there's no fuss. Using audi has been like using an NHS GP. It's a 2 to 3 week wait for an appointment, and even then you only get half the job done or have to be referred to someone else who has another 2 to 3 week waiting list.