Good to hear the flounge buffet is to be improved, that was always the biggest problem. However I do think the reasoning behind the afternoon tea is deeply flawed for two reasons:
1. As a major international hub flagship terminal it stands to reason that there are a large amount of transfer passengers in the lounge for whom it isn't 4pm, it's 1pm, or 8pm or some other time when they want a proper hot meal.
2. Most Brits with a normal appetite about to get on a flight leaving between 6 and 7pm are going to want to have their dinner between 5 and 6pm. Inflight catering is not reliable enough or large enough to provide a dinner when you might not be getting to your destination until late evening.
I can see where the afternoon tea idea is coming from but with only 3 choices of sandwich there is a good chance of finding there is nothing substantial that you like in order to fill up.