Unfortunately, HTC has been a bit more vague with the release of the OTA in Europe and has been forced to apologize for the delay from the rest of the world going into 2018.
We’re sorry for the delay in delivering your Oreo update for the HTC U11. We have started to roll out the update globally but have had some complexities that have caused a delay to our release in Europe. Please bear with us and we’ll let you know more as soon as we can.
— HTC UK (@HTC_UK) January 5, 2018
Those “complexities” could not be detailed and nether could an estimated time of arrival. The answer should be hopefully soon, but it can’t be guaranteed at this point.