I'm not in the UK but I have kept and bred chams in enclosures made of glass as well as enclosures made of screen.
For what it is worth- IMO either situation can result in a thriving chameleon.
And there is enough nonsense on both sides of the argument to go around. The US has a huge range of ambient humidity, with many of the members of the forums here living in true desert states much dryer than the UK that make my skin literally itch like crazy from dehydration about 20 minutes after I take a shower as the moisture is sucked from my easterner skin (states like nevada, Utah, Arizona, etc in the SW US). Most of the members in these states use screen enclosures.
I prefer screen because they are generally larger, cheaper and can be placed outdoors during the summer months.
But I never saw any problems from the "lack of airflow" in my glass tanks either and honestly believe such problems are superstitions that get parrotted over and over or perhaps have a grain of truth in someone horrible about husbandry- for example never cleaning the tank and allowing things to remain soggy all the time from improper and unnecessarily excessive water supply to the chameleon (my observation was that when I kept chams in glass, they tended to remain hydrated a little more easily and had a lower water requirement that could be satisified by a drip system into a catch bowl for 20-30 minutes a day, and a light misting a couple times a day for humidity)...
On the other hand, although I am a fan of screen cages nowadays, in the winter you may need to increase humidity somehow in a screen cage- either by wrapping it in plastic and reducing the airflow or running a humidifier in the same room, etc.
