My Fire and Rescue Service contact spoke to me tonight, sooner than I expected. He is a recently-retired deputy chief fire officer. I explained that the point of issue was the safety of wooden tea light holders, specifically the type I have made and which he has seen, which is a spindle-turned block of wood with a close-fitting hole for the tea light, with no liner.
He told me that he was well aware of the dangers of tea lights and had been directly involved in a tea light television fire which resulted in fatalities. He said, emphatically, that there was no risk of my type of tea light holder causing a fire and that wood was the best material to use to separare a tea light from a television. He commented that tea light fires are the result of the way candles are used, not the result of a wooden holder catching fire. He also commented that wood has a relatively low flammability in house fires - that is, compared with other materials found in houses.
I regret that I cannot provide a written statement to this effect, so I suppose this post has to be regarded as anecdote. I am content that I have taken well-qualified advice, so I am happy to continue doing what I do, thus saving the additional cost of glass inserts.
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People might be interested in a commentary by a professional woodturner on YouTube. Search for "a word about tea light candle safety"