I did stumble upon this ford near Twyford - which I found later via Google is quite notorious - see picture.
At the time the level indicator was showing ~0.4M - so within spec! As I hesitated a Land Cruiser steamed through and made quite a splash. So much so that I decided to turn around. Just wondered if I could have followed the LC or if being cautious was the right call.
Sounds like the LC was local and was showing off with his local knowledge.
Looking at that picture I think you would have been ok. In flood I wouldn't bother trying as you might float away.
The secret to water is not to enter with a big splash. If you don't know it you should at the very least get out and have a look....the biggest danger is driving off the tarmac into something very soft or very deep because you can't see it. On all the courses I've done they advise you to get wet and check it...fail safe.
Wait for the water to settle so don't follow another vehicle through particularly if it's making a big bow wave. Enter keep a steady slow speed aiming to push the water in front of you like a wave but not so fast that it's coming over the bonnet. This will create a gap in the water for your car. Keep going and don't stop because if it was a fraction too deep that wave you have created and vacumn will bite you in your air intake and all will be lost.
I would highly recommend doing an off road course. I doubt you'll find any with Q5s but LR have LR Experience centres all over the country. Good day out in someone elses car.