Some, like the Crowne Plaza in Marlow, will always upgrade you and give you Club Lounge access as a Platinum without you having to ask.

I asked and got upgraded at the CP in London, City, but wouldn't have got it without asking.

I had a row at a Holiday Inn (Portsmouth, UK) as they lied and said they were fully booked and had no better rooms. When I got to our standard room I checked online and they had executive room availablity, so I went back downstairs and stood my ground in reception till we got upgraded. Fact is, we preferred the original room, I think the manager deliberately gave us the worst of his so-called executive rooms.

My opinion is always ask, and if denied, make sure the reason is true!