Hi Tinkobell, I am happy to help however, it terms of whether this is 'a tricky one' trust me, it really really isn't.
If you can get that signature in the presence of a witness, you do it.
From what you are saying about him, you should have no qualms about it at all, (esp as until recently you say he was quite with it.)
This is the simple bit, getting LPA, relatively speaking.
Now, I should say that our experience was a tad different, as my mother had advanced Parkinson's and that isn't really the same as cancer of course in terms of how the State views it.
With cancer you go into remission or you don't.
It's either hip hip hooray and isn't the NHS wonderful, if not, well sadly nature takes its course. With Parkinson's, there is a grey area where folk can linger beyond what the State in terms of the local authority and NHS CCG is prepared to pay for, even if you are self-funding. That means - whisper it - covert dehydration programmes which the family won't be told about, to hasten their demise.
Now, you aren't in that situation.
However, if you were in our situ, it's a case where they simply won't let you have your parent back to the family home, because then they relinquish control. So it's a case of, you want to keep your parent alive by giving drink, you do it - by visiting the care home and forking out a grand a week for two years to do it.
In other cases, well, the authorities don't mind your having a relative back to the family home - to die. They just mind when it comes to having them back to the family home - to live.
But in either case - and particularly ours - the local Council is the decision maker for your relative's care. Not you, not once they are deemed to have lost mental capacity.
And often the local Council are the most corrupt and bent people you will ever meet in your lives - you really don't want them - or the NHS - getting their hooks into your parent.
I say all this because you still seem to be doing the 'going by the book' bit where you are being a bit too 'honest' and painstaking about the situation, like, well, dunno, he was a bit off today so maybe we won't get LPA. If you can get it, do it.