I have come to the conclusion that manufacturers of things such as these and shower/body washes aren't covered by the disability act (or whatever its latest name is).
I understand why they use bottles containing 400ml/500ml - it is more profitable for them. Unfortunately for those of us who have hand/finger/wrist problems these size bottles are almost impossible to use. Usually half of the contents end up down the drain because we constantly drop them.
Another thought which I have is, that when you are under the shower your hands are wet.....
No point in complaining to Trading Standards, is there?