Welcome to FT, QED99!
LHR used to be terrible in the past: no OLCI available and they insisted on weighing even the smallest carry-ons. Nowadays, I never go to the check-in desk there. Thank God for OLCI!
If you weren't travelling alone, I guess you could have had your travelling companion stand behind the corner, secretly guarding your extra bag while you were checking in, and vice versa.