score:9
Compiling comments into an answer:
First hand experience of this being allowed in Eurostar queues.
You can use either queue. The IO you spoke with was likely annoyed because you made more work for him. Ignore it. Or speak with the duty CIO. (per comments above).
See also the Chief Inspector's report "An inspection of border control at Manchester Airport"
See also Ministerial Statement on E-Borders
Related answer saying the same thing but covering more scenarios: Non-EU citizen travelling to UK with EU citizen friend, which queue to use?
Related answer regarding non-EU family members and queues: Which queue for a EU/non-EU couple travelling through UK Immigration Control together?
Yet another related answer: Other passports queue arriving in UK?
Vaguely related (i.e., no queue): What happens when someone inadvertently enters the UK without a landing interview?