"Payment must be made in full with an American Express Card in the Platinum Card Member's or Centurion® Member’s name"
Yes the above language definitely appears in UK FHR confirmations as well. Whether that is enforced by the hotel is another question. Especially as discussed above since the UK site allows for all of the traveller/guest details to be customized to the person actually staying in the hotel. If that person then produces an Amex in their name at checkout I wonder if there would be any issues.
I suspect this may be a real YMMV depending on how meticulous an individual hotel is...