I was there in June on a paid stay. Got a very nice room, w/chocolate and a sm. bottle of water. Upon check-in, I was told that I didn't need any b'fast voucher. That was a misunderstanding; I had to ask again in the morning and had to produce the copy of the rules. The young reception clerk went to the manager, and returned saying: "Ok, for this time"... Groan...
Very nice b'fast, but expensive (16 GBP). Upon checking out, I had to ask again to have the b'fast charges removed, which was done promptly.
During the same period I also stayed at the Hilton in Holland Park (Kensington Hilton). We arrived late (at 11 pm), and the reception clerk gave us a tiny room up on the executive floor. The b'fast there was also excellent, and had the added advantage that it didn't require begging.
All else being equal, I'd prefer to avoid properties where I have to beg or fight for b'fast.