It does vary from place to place, but AMS certainly isn't your problem, nor is LHR T5, T3 or LGW due to the self tagging machines there. LCY is also busy but slick, a 10 minute queue is long for them. You should allow an hour before departure at check-in, simply due to the long walk to D26 or whereever the BA departs from, it's one of the longest airport hikes this side of Bangkok.

I'm guessing your previous experiences were on low cost carriers, they generally do have a bit of a queue built into the "system", but 45 minutes would be at the top end. Holiday peaks, charters and ski resorts bring in longer times.

But it's the sort of thing that makes me a hand baggage only traveller, and I can manage for 3 or 4 weeks without needing a bag to check in. If the bag isn't obscenely large you could also consider just checking it in at the gate instead.