Bit OT because not in London, but the CP Manchester Airport specifically told me that club room upgrade and club access were an Ambassador benefit, not a Platinum benefit (although not clear whether it was Amb or RA). However, on my last stay (last week) I got the club room upgrade, but not club access, and was told that the policy had changed months ago - so it seems to be at the whim of the person checking you in.

CP Manchester also used to give club access to RAs, but appear to have stopped now.

The new HIX in Manchester have never heard of Ambassador/RA, and tried to tell me that my card was for a different hotel chain - they then tried to persuade me to sign up for Priority Club membership (I know, it's a HIX, but you would think that the training programme at least mentioned it).