Great question — answering as the UphillTech team:
T3 landside has a pub that does a Full English - The Oceanic. You won't beat that sort of thing for a big breakfast at the airport. T2 has an equivalent, the Queens Arms, also landside. So your best bet could be to eat before security. But T3 also has Spuntino in departures "For breakfast, tuck in to ... classic proper English breakfast." If none of those will do, you'll need to get something before heading to the airport, as the options are pretty similar between the 2 terminals
Full answer by Chris H - UK: https://travel.stackexchange.com/a/183013 (CC BY-SA 4.0).
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