We ended up in the United lounge and found it to be very good in all respects. Good quality hot food options, including a traditional British style cooked breakfast, and the champagne was very acceptable.
Just to round off, very good in flight service by Thai Airways on all legs. A somewhat exciting final leg into Heathrow as I reckon we were about 3 seconds from landing when there was a tremendous surge of power from the aircraft as the landing was aborted and we went round for another go. Another aircraft still on the runway according to the captain. All very professionally handled of course.