This is interesting, as most of the FS Marriotts I stay at in London offer the choice for Plats of breakfast in the lounge (great when I am on-the-go to a client meeting) or full English in the restaurant (ideal for a lazy weekend morning). I would be very sorry to see that choice be eliminated. Especially since many UK Marriotts sell rooms with access to the Lounge, so you get a lot of people eating breakfast in there as part of their room rate.

I'm not sure when my next London trip will be, likely end of August/early September and will report back. I typically stay at the Kensington Marriott, as it fits under my corporate hotel cap for London.