I just got back from Brussels - GREAT trip!
The 'lounge' in London does take the Amex plat to get in. For a morning train there was juice, tea, coffee and water to drink, cookies and croissants to snack on and various newspapers. There were also (most importantly) comfortable chairs and no crowds!
I do wish that it worked in Brussels. That is one nasty waiting area, especially when I arrived too early!
I am not sure if it falls in the Eurostar FAQ, but there doesn't seem to be a Frequent Traveler forum

. Can I use Amex transfer points for a Carte Blanche?
Thanks for the help
Dr> PITUK