Doctors being humans sometimes make errors, here on the "untreatable" part. Still: good food and good drinks should always be amongst the options for treatment. Enjoy them!
Bristol Royal infirmary is very well regarded, but your caution Jerome is even more prescient and worth attention in this circumstance. When a Dr. says “brain tumor” he may mean metastatic cancer from another organ, (and too advanced) or else a primary brain tumor. Each has so many variables that a second opinion is always worthwhile!
I can recommend, in London, Stuart, The Royal Marsden Hospital is a first-class Tertiary Cancer Center with far more capabilities than most other centers in Europe and if appropriate and feasible, a second opinion there would ease my mind.
My sister had “fatal” metastatic colon cancer treated at The Royal Marsden some 30 years ago, (amazingly by their kind generous cooperation and professional respect), under my direction and then retreated twice there when it recurred and utterly cured for the last 18 years!
All cases are totally different and it could be that you already have the very wisest advice from Bristol but still, with a brain expressing such humanity and bonding as yours, the extra effort seems worthwhile!
Asher