I've only flown once as an adult, but have flown about 4 or 5 times as a child. Couldn't really tell you what those experiences were like.
When I flew as an Adult it was all fine leaving from Britain.
We left from Bristol however, which is a significantly smaller airport than any of the London ones, like Heathrow or Gatwick.
On the way out there were no problems. Emptied my items onto the tray, and walked through the scanner with no problems.
On the way back, from Rome's Fiumicino airport was a little more awkward.
All my stuff went on the tray and through fine.
But then as I went through the scanner it beeped, and I had to walk back through.
Then it beeped as he sent me through once more.
Then I had to take off my shoes, which was awkward, because they're both double-knotted, and take what seems like an eternity (or does when you have 50 irate Italians behind you) to take off.
Anyway, I walked through holding them in front of me this time, it beeped as they went through, and then the guards let me carry on.
So, in other words, no issue at all.
But it makes you nervous eitherway.
And there were no problems with the fact that I had a dagger stored in my suitcase.