HMRC are consulting on "how the tax treatment of travel and subsistence expenses could be simplified or improved". Essentially the plan for this simplification is probably just to stop employees/directors getting tax relief for subsistence when working away from their usual workplace, meaning the tax bills of those who are somewhat itinerant going up a bit.
This seems harsh on the face of it, but there is a logic to it. The rules really relate back to the days when it was expected that most employees would be fed in a work canteen - the ability to reimburse those who were working away tax-free was just supposed to level the playing field. These days, not that many employees get to eat for free in the canteen.
If you've strong feelings about it, you can give HMRC your thoughts! We don't, so we won't, but there's more detail here:
https://www.gov.uk/government/consultations/travel-and-subsistence-review