Says you can get tax relief to pay for a glucometer if prescribed by a doctor. Of course, if a doctor prescribed it you wouldn't be paying for it (sigh).
Unfortunately my google fu has failed to find any mention of this on the inland revenue website...
If you find out that this is a possibility I suspect a number of UK dexcom users would find it helpful. (Given the cost of a dexcom, I suspect not many will be self funding without earning enough to pay tax.)
In Canada (province of Ontario), I get my libre essentially for free, because I am older than 65. I am prescribed a libre because I am insulin dependent. Also, if one has to pay for it, there are no sales taxes (provincially or federal) on it. One can also claim any payment as a medical credit on one's income tax return, which may reduce one's income tax a bit.