I have recently stayed in this hotel five times in the last couple of months. I am only gold, so don't really expect much. But I have never had an upgrade. Although, I always checkin online, I think this limits my chances. I also received a card from reception about my preferences for future stays. I have filled this in twice now and have never been given what I put down on the card (ie 2 bottles of sparkling water instead of one still & one sparkling).
Some of the rooms are dated. I have found that some are more modern than others with newer TV's and newer furniture. Four of my stays I was told that parking was complementary and one stay I was asked to pay £5, so I really dont know which is true.
Breakfast is fine. I have definitely seen both better and worse in UK Hiltons.
The gym is ok and the pool is a nice touch.