I recently travelled from Athens to Luton and back. In Athens I queued up at check-in and they verified me (with a sticker added to the back of my passport) and this meant they didn't need to verify me before entering the gate area (some were verified when entering the gate area, so check-in desk didn't seem to be mandatory). In Luton, the queue for Athens was long (due to lots of checked luggage) so I asked at a less busy check-in desk and they told me I could get verified at the gate too, which is what I did (no stickers, just let through). I'd say it's worth first popping around to a check-in desk to get it done there if it's not busy.