Tips, if you don't mind me suggesting them.
You are right that crew might assume most passengers want to sleep and not eat. But you are entitled to have a full meal.
I suggest that when then you order, you say yes please I'd like dinner in an enthusiastic way. Also for drinks, ask for an aperitif then wine, (eg I'd like a gin a tonic now please and then wine with dinner).
The crew should then get the gist and keep you happy.
And, TBH unless you land in the afternoon at LHR , skip the breakfast on board and go and have breakfast in the T5 arrivals lounge (or T3 AA arrivals lounge) which is much better.