So we stayed at St Ermin's last night. We had a family room booked and were upgraded to a suite. All 4 of us (2 adults, 2 kids) got free breakfast and we got a bottle of prosecco and some truffles for our 10th wedding anniversary. Managed to get an extra hour as late checkout. Lovely hotel, great room, great breakfast (apart from out-of-date yoghurts), great location, great treatment as Marriott Gold. Definitely considering keeping my points to stay here again next time we go to the theatre. Would recommend to those looking for a room for 4 in central London.
The only 2 minor negative points were that the room windows are all "whited" out, so the only natural light is if you open them. Also, I dealt with 3 receptionists and all seemed to be non-native English speakers and I struggled a little bit to understand them. I think front-of-house is important in high quality hotels. I felt the reception staff had patchy English and this didn't give the same level of experience the rest of the hotel seemed to be trying and managing to give.