When I read your first post I imagined larger containers. If they were 4 ozs (just over 100ml) it does seem you've come across a jobsworth who has decided to go strictly by the book.

To stray off the point slightly, a letter from your specialist could easily be mocked up and security can't really put any faith in it.

I discovered this a few years ago when I had a lot of metalwork put in my leg which my consultant reckoned would set off every airport scanner. When I mentioned him supplying a letter of explanation, he said the medical profession had discussed such a scenario with the security authorities. The outcome was that no letter would be worth the paper it was printed on, and that security would have to satisfy themselves that I posed no threat.